From 89c30a00a71988c8db632f8f3cc94ed241bdaa1f Mon Sep 17 00:00:00 2001
From: alecpl <alec@alec.pl>
Date: Sun, 01 Jan 2012 07:26:08 -0500
Subject: [PATCH] - Don't load jqueryui plugin, it's required now by default - Move datepicker's date format setting to the plugin

---
 program/include/rcube_imap.php | 2500 +++++++++++++++++++++-------------------------------------
 1 files changed, 913 insertions(+), 1,587 deletions(-)

diff --git a/program/include/rcube_imap.php b/program/include/rcube_imap.php
index c2a4a0d..2a2f203 100644
--- a/program/include/rcube_imap.php
+++ b/program/include/rcube_imap.php
@@ -5,7 +5,8 @@
  | program/include/rcube_imap.php                                        |
  |                                                                       |
  | This file is part of the Roundcube Webmail client                     |
- | Copyright (C) 2005-2010, The Roundcube Dev Team                       |
+ | Copyright (C) 2005-2011, The Roundcube Dev Team                       |
+ | Copyright (C) 2011, Kolab Systems AG                                  |
  | Licensed under the GNU GPL                                            |
  |                                                                       |
  | PURPOSE:                                                              |
@@ -31,7 +32,6 @@
  */
 class rcube_imap
 {
-    public $debug_level = 1;
     public $skip_deleted = false;
     public $page_size = 10;
     public $list_page = 1;
@@ -47,11 +47,11 @@
     public $conn;
 
     /**
-     * Instance of rcube_mdb2
+     * Instance of rcube_imap_cache
      *
-     * @var rcube_mdb2
+     * @var rcube_imap_cache
      */
-    private $db;
+    private $mcache;
 
     /**
      * Instance of rcube_cache
@@ -59,6 +59,14 @@
      * @var rcube_cache
      */
     private $cache;
+
+    /**
+     * Internal (in-memory) cache
+     *
+     * @var array
+     */
+    private $icache = array();
+
     private $mailbox = 'INBOX';
     private $delimiter = NULL;
     private $namespace = NULL;
@@ -67,8 +75,6 @@
     private $default_charset = 'ISO-8859-1';
     private $struct_charset = NULL;
     private $default_folders = array('INBOX');
-    private $messages_caching = false;
-    private $icache = array();
     private $uid_id_map = array();
     private $msg_headers = array();
     public  $search_set = NULL;
@@ -77,27 +83,25 @@
     private $search_sort_field = '';
     private $search_threads = false;
     private $search_sorted = false;
-    private $db_header_fields = array('idx', 'uid', 'subject', 'from', 'to', 'cc', 'date', 'size');
     private $options = array('auth_method' => 'check');
     private $host, $user, $pass, $port, $ssl;
+    private $caching = false;
+    private $messages_caching = false;
 
     /**
      * All (additional) headers used (in any way) by Roundcube
-     * Not listed here: DATE, FROM, TO, SUBJECT, CONTENT-TYPE, LIST-POST
+     * Not listed here: DATE, FROM, TO, CC, REPLY-TO, SUBJECT, CONTENT-TYPE, LIST-POST
      * (used for messages listing) are hardcoded in rcube_imap_generic::fetchHeaders()
      *
      * @var array
      * @see rcube_imap::fetch_add_headers
      */
     private $all_headers = array(
-        'REPLY-TO',
         'IN-REPLY-TO',
-        'CC',
         'BCC',
         'MESSAGE-ID',
         'CONTENT-TRANSFER-ENCODING',
         'REFERENCES',
-        'X-PRIORITY',
         'X-DRAFT-INFO',
         'MAIL-FOLLOWUP-TO',
         'MAIL-REPLY-TO',
@@ -171,12 +175,13 @@
         $attempt = 0;
         do {
             $data = rcmail::get_instance()->plugins->exec_hook('imap_connect',
-                array('host' => $host, 'user' => $user, 'attempt' => ++$attempt));
+                array_merge($this->options, array('host' => $host, 'user' => $user,
+                    'attempt' => ++$attempt)));
 
             if (!empty($data['pass']))
                 $pass = $data['pass'];
 
-            $this->conn->connect($data['host'], $data['user'], $pass, $this->options);
+            $this->conn->connect($data['host'], $data['user'], $pass, $data);
         } while(!$this->conn->connected() && $data['retry']);
 
         $this->host = $data['host'];
@@ -215,6 +220,8 @@
     function close()
     {
         $this->conn->closeConnection();
+        if ($this->mcache)
+            $this->mcache->close();
     }
 
 
@@ -306,6 +313,19 @@
     function set_options($opt)
     {
         $this->options = array_merge($this->options, (array)$opt);
+    }
+
+
+    /**
+     * Activate/deactivate debug mode
+     *
+     * @param boolean $dbg True if IMAP conversation should be logged
+     * @access public
+     */
+    function set_debug($dbg = true)
+    {
+        $this->options['debug'] = $dbg;
+        $this->conn->setDebug($dbg, array($this, 'debug_handler'));
     }
 
 
@@ -411,40 +431,39 @@
      * Save a set of message ids for future message listing methods
      *
      * @param  string  IMAP Search query
-     * @param  array   List of message ids or NULL if empty
+     * @param  rcube_result_index|rcube_result_thread  Result set
      * @param  string  Charset of search string
      * @param  string  Sorting field
      * @param  string  True if set is sorted (SORT was used for searching)
      */
-    function set_search_set($str=null, $msgs=null, $charset=null, $sort_field=null, $threads=false, $sorted=false)
+    function set_search_set($str=null, $msgs=null, $charset=null, $sort_field=null, $sorted=false)
     {
-        if (is_array($str) && $msgs == null)
-            list($str, $msgs, $charset, $sort_field, $threads) = $str;
-        if ($msgs === false)
-            $msgs = array();
-        else if ($msgs != null && !is_array($msgs))
-            $msgs = explode(',', $msgs);
+        if (is_array($str) && $msgs === null)
+            list($str, $msgs, $charset, $sort_field, $sorted) = $str;
 
         $this->search_string     = $str;
         $this->search_set        = $msgs;
         $this->search_charset    = $charset;
         $this->search_sort_field = $sort_field;
-        $this->search_threads    = $threads;
         $this->search_sorted     = $sorted;
+        $this->search_threads    = is_a($this->search_set, 'rcube_result_thread');
     }
 
 
     /**
      * Return the saved search set as hash array
+     *
+     * @param bool $clone Clone result object
+     *
      * @return array Search set
      */
     function get_search_set()
     {
-        return array($this->search_string,
+        return array(
+            $this->search_string,
 	        $this->search_set,
         	$this->search_charset,
         	$this->search_sort_field,
-        	$this->search_threads,
         	$this->search_sorted,
 	    );
     }
@@ -458,7 +477,7 @@
      */
     function get_mailbox_name()
     {
-        return $this->conn->connected() ? $this->mailbox : '';
+        return $this->mailbox;
     }
 
 
@@ -669,10 +688,10 @@
 
         // count search set
         if ($this->search_string && $mailbox == $this->mailbox && ($mode == 'ALL' || $mode == 'THREADS') && !$force) {
-            if ($this->search_threads)
-                return $mode == 'ALL' ? count((array)$this->search_set['depth']) : count((array)$this->search_set['tree']);
+            if ($mode == 'ALL')
+                return $this->search_set->countMessages();
             else
-                return count((array)$this->search_set);
+                return $this->search_set->count();
         }
 
         $a_mailbox_cache = $this->get_cache('messagecount');
@@ -685,12 +704,13 @@
             $a_mailbox_cache[$mailbox] = array();
 
         if ($mode == 'THREADS') {
-            $res   = $this->_threadcount($mailbox, $msg_count);
-            $count = $res['count'];
+            $res   = $this->fetch_threads($mailbox, $force);
+            $count = $res->count();
 
             if ($status) {
-                $this->set_folder_stats($mailbox, 'cnt', $res['msgcount']);
-                $this->set_folder_stats($mailbox, 'maxuid', $res['maxuid'] ? $this->_id2uid($res['maxuid'], $mailbox) : 0);
+                $msg_count = $res->countMessages();
+                $this->set_folder_stats($mailbox, 'cnt', $msg_count);
+                $this->set_folder_stats($mailbox, 'maxuid', $msg_count ? $this->id2uid($msg_count, $mailbox) : 0);
             }
         }
         // RECENT count is fetched a bit different
@@ -701,7 +721,6 @@
         else if ($this->skip_deleted) {
             $search_str = "ALL UNDELETED";
             $keys       = array('COUNT');
-            $need_uid   = false;
 
             if ($mode == 'UNSEEN') {
                 $search_str .= " UNSEEN";
@@ -712,24 +731,23 @@
                 }
                 if ($status) {
                     $keys[]   = 'MAX';
-                    $need_uid = true;
                 }
             }
 
+            // @TODO: if $force==false && $mode == 'ALL' we could try to use cache index here
+
             // get message count using (E)SEARCH
             // not very performant but more precise (using UNDELETED)
-            $index = $this->conn->search($mailbox, $search_str, $need_uid, $keys);
-
-            $count = is_array($index) ? $index['COUNT'] : 0;
+            $index = $this->conn->search($mailbox, $search_str, true, $keys);
+            $count = $index->count();
 
             if ($mode == 'ALL') {
-                if ($need_uid && $this->messages_caching) {
-                    // Save messages index for check_cache_status()
-                    $this->icache['all_undeleted_idx'] = $index['ALL'];
-                }
+                // Cache index data, will be used in message_index_direct()
+                $this->icache['undeleted_idx'] = $index;
+
                 if ($status) {
                     $this->set_folder_stats($mailbox, 'cnt', $count);
-                    $this->set_folder_stats($mailbox, 'maxuid', is_array($index) ? $index['MAX'] : 0);
+                    $this->set_folder_stats($mailbox, 'maxuid', $index->max());
                 }
             }
         }
@@ -740,7 +758,7 @@
                 $count = $this->conn->countMessages($mailbox);
                 if ($status) {
                     $this->set_folder_stats($mailbox,'cnt', $count);
-                    $this->set_folder_stats($mailbox, 'maxuid', $count ? $this->_id2uid($count, $mailbox) : 0);
+                    $this->set_folder_stats($mailbox, 'maxuid', $count ? $this->id2uid($count, $mailbox) : 0);
                 }
             }
         }
@@ -755,40 +773,6 @@
 
 
     /**
-     * Private method for getting nr of threads
-     *
-     * @param string $mailbox   Folder name
-     *
-     * @returns array Array containing items: 'count' - threads count,
-     *                'msgcount' = messages count, 'maxuid' = max. UID in the set
-     * @access  private
-     */
-    private function _threadcount($mailbox)
-    {
-        $result = array();
-
-        if (!empty($this->icache['threads'])) {
-            $dcount = count($this->icache['threads']['depth']);
-            $result = array(
-                'count'    => count($this->icache['threads']['tree']),
-                'msgcount' => $dcount,
-                'maxuid'   => $dcount ? max(array_keys($this->icache['threads']['depth'])) : 0,
-            );
-        }
-        else if (is_array($result = $this->_fetch_threads($mailbox))) {
-            $dcount = count($result[1]);
-            $result = array(
-                'count'    => count($result[0]),
-                'msgcount' => $dcount,
-                'maxuid'   => $dcount ? max(array_keys($result[1])) : 0,
-            );
-        }
-
-        return $result;
-    }
-
-
-    /**
      * Public method for listing headers
      * convert mailbox name with root dir first
      *
@@ -797,16 +781,17 @@
      * @param   string   $sort_field Header field to sort by
      * @param   string   $sort_order Sort order [ASC|DESC]
      * @param   int      $slice      Number of slice items to extract from result array
+     *
      * @return  array    Indexed array with message header objects
      * @access  public
      */
-    function list_headers($mailbox='', $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
+    public function list_headers($mailbox='', $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
     {
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
         }
 
-        return $this->_list_headers($mailbox, $page, $sort_field, $sort_order, false, $slice);
+        return $this->_list_headers($mailbox, $page, $sort_field, $sort_order, $slice);
     }
 
 
@@ -818,123 +803,46 @@
      * @param   string   $sort_field Header field to sort by
      * @param   string   $sort_order Sort order [ASC|DESC]
      * @param   int      $slice      Number of slice items to extract from result array
+     *
      * @return  array    Indexed array with message header objects
-     * @access  private
      * @see     rcube_imap::list_headers
      */
-    private function _list_headers($mailbox='', $page=NULL, $sort_field=NULL, $sort_order=NULL, $recursive=false, $slice=0)
+    private function _list_headers($mailbox='', $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
     {
-        if (!strlen($mailbox))
+        if (!strlen($mailbox)) {
             return array();
+        }
+
+        $this->set_sort_order($sort_field, $sort_order);
+        $page = $page ? $page : $this->list_page;
 
         // use saved message set
-        if ($this->search_string && $mailbox == $this->mailbox)
-            return $this->_list_header_set($mailbox, $page, $sort_field, $sort_order, $slice);
-
-        if ($this->threading)
-            return $this->_list_thread_headers($mailbox, $page, $sort_field, $sort_order, $recursive, $slice);
-
-        $this->_set_sort_order($sort_field, $sort_order);
-
-        $page         = $page ? $page : $this->list_page;
-        $cache_key    = $mailbox.'.msg';
-
-        if ($this->messages_caching) {
-            // cache is OK, we can get messages from local cache
-            // (assume cache is in sync when in recursive mode)
-            if ($recursive || $this->check_cache_status($mailbox, $cache_key)>0) {
-                $start_msg = ($page-1) * $this->page_size;
-                $a_msg_headers = $this->get_message_cache($cache_key, $start_msg,
-                    $start_msg+$this->page_size, $this->sort_field, $this->sort_order);
-                $result = array_values($a_msg_headers);
-                if ($slice)
-                    $result = array_slice($result, -$slice, $slice);
-                return $result;
-            }
-            // cache is incomplete, sync it (all messages in the folder)
-            else if (!$recursive) {
-                $this->sync_header_index($mailbox);
-                return $this->_list_headers($mailbox, $page, $this->sort_field, $this->sort_order, true, $slice);
-            }
+        if ($this->search_string && $mailbox == $this->mailbox) {
+            return $this->_list_header_set($mailbox, $page, $slice);
         }
 
-        // retrieve headers from IMAP
-        $a_msg_headers = array();
-
-        // use message index sort as default sorting (for better performance)
-        if (!$this->sort_field) {
-            if ($this->skip_deleted) {
-                // @TODO: this could be cached
-                if ($msg_index = $this->_search_index($mailbox, 'ALL UNDELETED')) {
-                    $max = max($msg_index);
-                    list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
-                    $msg_index = array_slice($msg_index, $begin, $end-$begin);
-                }
-            }
-            else if ($max = $this->conn->countMessages($mailbox)) {
-                list($begin, $end) = $this->_get_message_range($max, $page);
-                $msg_index = range($begin+1, $end);
-            }
-            else
-                $msg_index = array();
-
-            if ($slice && $msg_index)
-                $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);
-
-            // fetch reqested headers from server
-            if ($msg_index)
-                $this->_fetch_headers($mailbox, join(",", $msg_index), $a_msg_headers, $cache_key);
-        }
-        // use SORT command
-        else if ($this->get_capability('SORT') &&
-            // Courier-IMAP provides SORT capability but allows to disable it by admin (#1486959)
-            ($msg_index = $this->conn->sort($mailbox, $this->sort_field, $this->skip_deleted ? 'UNDELETED' : '')) !== false
-        ) {
-            if (!empty($msg_index)) {
-                list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
-                $max = max($msg_index);
-                $msg_index = array_slice($msg_index, $begin, $end-$begin);
-
-                if ($slice)
-                    $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);
-
-                // fetch reqested headers from server
-                $this->_fetch_headers($mailbox, join(',', $msg_index), $a_msg_headers, $cache_key);
-            }
-        }
-        // fetch specified header for all messages and sort
-        else if ($a_index = $this->conn->fetchHeaderIndex($mailbox, "1:*", $this->sort_field, $this->skip_deleted)) {
-            asort($a_index); // ASC
-            $msg_index = array_keys($a_index);
-            $max = max($msg_index);
-            list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
-            $msg_index = array_slice($msg_index, $begin, $end-$begin);
-
-            if ($slice)
-                $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);
-
-            // fetch reqested headers from server
-            $this->_fetch_headers($mailbox, join(",", $msg_index), $a_msg_headers, $cache_key);
+        if ($this->threading) {
+            return $this->_list_thread_headers($mailbox, $page, $slice);
         }
 
-        // delete cached messages with a higher index than $max+1
-        // Changed $max to $max+1 to fix this bug : #1484295
-        $this->clear_message_cache($cache_key, $max + 1);
+        // get UIDs of all messages in the folder, sorted
+        $index = $this->message_index($mailbox, $this->sort_field, $this->sort_order);
 
-        // kick child process to sync cache
-        // ...
-
-        // return empty array if no messages found
-        if (!is_array($a_msg_headers) || empty($a_msg_headers))
+        if ($index->isEmpty()) {
             return array();
+        }
 
-        // use this class for message sorting
-        $sorter = new rcube_header_sorter();
-        $sorter->set_sequence_numbers($msg_index);
-        $sorter->sort_headers($a_msg_headers);
+        $from = ($page-1) * $this->page_size;
+        $to   = $from + $this->page_size;
 
-        if ($this->sort_order == 'DESC')
-            $a_msg_headers = array_reverse($a_msg_headers);
+        $index->slice($from, $to - $from);
+
+        if ($slice)
+            $index->slice(-$slice, $slice);
+
+        // fetch reqested messages headers
+        $a_index = $index->get();
+        $a_msg_headers = $this->fetch_headers($mailbox, $a_index);
 
         return array_values($a_msg_headers);
     }
@@ -945,113 +853,85 @@
      *
      * @param   string   $mailbox    Mailbox/folder name
      * @param   int      $page       Current page to list
-     * @param   string   $sort_field Header field to sort by
-     * @param   string   $sort_order Sort order [ASC|DESC]
-     * @param   boolean  $recursive  True if called recursively
      * @param   int      $slice      Number of slice items to extract from result array
+     *
      * @return  array    Indexed array with message header objects
-     * @access  private
      * @see     rcube_imap::list_headers
      */
-    private function _list_thread_headers($mailbox, $page=NULL, $sort_field=NULL, $sort_order=NULL, $recursive=false, $slice=0)
+    private function _list_thread_headers($mailbox, $page, $slice=0)
     {
-        $this->_set_sort_order($sort_field, $sort_order);
+        // get all threads (not sorted)
+        if ($mcache = $this->get_mcache_engine())
+            $threads = $mcache->get_thread($mailbox);
+        else
+            $threads = $this->fetch_threads($mailbox);
 
-        $page = $page ? $page : $this->list_page;
-//    $cache_key = $mailbox.'.msg';
-//    $cache_status = $this->check_cache_status($mailbox, $cache_key);
-
-        // get all threads (default sort order)
-        list ($thread_tree, $msg_depth, $has_children) = $this->_fetch_threads($mailbox);
-
-        if (empty($thread_tree))
-            return array();
-
-        $msg_index = $this->_sort_threads($mailbox, $thread_tree);
-
-        return $this->_fetch_thread_headers($mailbox,
-            $thread_tree, $msg_depth, $has_children, $msg_index, $page, $slice);
+        return $this->_fetch_thread_headers($mailbox, $threads, $page, $slice);
     }
 
 
     /**
-     * Private method for fetching threads data
+     * Method for fetching threads data
      *
-     * @param   string   $mailbox Mailbox/folder name
-     * @return  array    Array with thread data
-     * @access  private
+     * @param  string $mailbox  Folder name
+     * @param  bool   $force    Use IMAP server, no cache
+     *
+     * @return rcube_imap_thread Thread data object
      */
-    private function _fetch_threads($mailbox)
+    function fetch_threads($mailbox, $force = false)
     {
+        if (!$force && ($mcache = $this->get_mcache_engine())) {
+            // don't store in self's internal cache, cache has it's own internal cache
+            return $mcache->get_thread($mailbox);
+        }
+
         if (empty($this->icache['threads'])) {
             // get all threads
             $result = $this->conn->thread($mailbox, $this->threading,
-                $this->skip_deleted ? 'UNDELETED' : '');
+                $this->skip_deleted ? 'UNDELETED' : '', true);
 
             // add to internal (fast) cache
-            $this->icache['threads'] = array();
-            $this->icache['threads']['tree'] = is_array($result) ? $result[0] : array();
-            $this->icache['threads']['depth'] = is_array($result) ? $result[1] : array();
-            $this->icache['threads']['has_children'] = is_array($result) ? $result[2] : array();
+            $this->icache['threads'] = $result;
         }
 
-        return array(
-            $this->icache['threads']['tree'],
-            $this->icache['threads']['depth'],
-            $this->icache['threads']['has_children'],
-        );
+        return $this->icache['threads'];
     }
 
 
     /**
      * Private method for fetching threaded messages headers
      *
-     * @param string  $mailbox      Mailbox name
-     * @param array   $thread_tree  Thread tree data
-     * @param array   $msg_depth    Thread depth data
-     * @param array   $has_children Thread children data
-     * @param array   $msg_index    Messages index
-     * @param int     $page         List page number
-     * @param int     $slice        Number of threads to slice
+     * @param string              $mailbox    Mailbox name
+     * @param rcube_result_thread $threads    Threads data object
+     * @param int                 $page       List page number
+     * @param int                 $slice      Number of threads to slice
+     *
      * @return array  Messages headers
      * @access  private
      */
-    private function _fetch_thread_headers($mailbox, $thread_tree, $msg_depth, $has_children, $msg_index, $page, $slice=0)
+    private function _fetch_thread_headers($mailbox, $threads, $page, $slice=0)
     {
-        $cache_key = $mailbox.'.msg';
-        // now get IDs for current page
-        list($begin, $end) = $this->_get_message_range(count($msg_index), $page);
-        $msg_index = array_slice($msg_index, $begin, $end-$begin);
+        // Sort thread structure
+        $this->sort_threads($threads);
+
+        $from = ($page-1) * $this->page_size;
+        $to   = $from + $this->page_size;
+
+        $threads->slice($from, $to - $from);
 
         if ($slice)
-            $msg_index = array_slice($msg_index, ($this->sort_order == 'DESC' ? 0 : -$slice), $slice);
+            $threads->slice(-$slice, $slice);
 
-        if ($this->sort_order == 'DESC')
-            $msg_index = array_reverse($msg_index);
-
-        // flatten threads array
-        // @TODO: fetch children only in expanded mode (?)
-        $all_ids = array();
-        foreach ($msg_index as $root) {
-            $all_ids[] = $root;
-            if (!empty($thread_tree[$root]))
-                $all_ids = array_merge($all_ids, array_keys_recursive($thread_tree[$root]));
-        }
+        // Get UIDs of all messages in all threads
+        $a_index = $threads->get();
 
         // fetch reqested headers from server
-        $this->_fetch_headers($mailbox, $all_ids, $a_msg_headers, $cache_key);
+        $a_msg_headers = $this->fetch_headers($mailbox, $a_index);
 
-        // return empty array if no messages found
-        if (!is_array($a_msg_headers) || empty($a_msg_headers))
-            return array();
-
-        // use this class for message sorting
-        $sorter = new rcube_header_sorter();
-        $sorter->set_sequence_numbers($all_ids);
-        $sorter->sort_headers($a_msg_headers);
+        unset($a_index);
 
         // Set depth, has_children and unread_children fields in headers
-        $this->_set_thread_flags($a_msg_headers, $msg_depth, $has_children);
+        $this->_set_thread_flags($a_msg_headers, $threads);
 
         return array_values($a_msg_headers);
     }
@@ -1061,30 +941,31 @@
      * Private method for setting threaded messages flags:
      * depth, has_children and unread_children
      *
-     * @param  array  $headers      Reference to headers array indexed by message ID
-     * @param  array  $msg_depth    Array of messages depth indexed by message ID
-     * @param  array  $msg_children Array of messages children flags indexed by message ID
-     * @return array   Message headers array indexed by message ID
+     * @param  array             $headers Reference to headers array indexed by message UID
+     * @param  rcube_imap_result $threads Threads data object
+     *
+     * @return array Message headers array indexed by message UID
      * @access private
      */
-    private function _set_thread_flags(&$headers, $msg_depth, $msg_children)
+    private function _set_thread_flags(&$headers, $threads)
     {
         $parents = array();
 
-        foreach ($headers as $idx => $header) {
-            $id = $header->id;
-            $depth = $msg_depth[$id];
+        list ($msg_depth, $msg_children) = $threads->getThreadData();
+
+        foreach ($headers as $uid => $header) {
+            $depth = $msg_depth[$uid];
             $parents = array_slice($parents, 0, $depth);
 
             if (!empty($parents)) {
-                $headers[$idx]->parent_uid = end($parents);
-                if (!$header->seen)
+                $headers[$uid]->parent_uid = end($parents);
+                if (empty($header->flags['SEEN']))
                     $headers[$parents[0]]->unread_children++;
             }
-            array_push($parents, $header->uid);
+            array_push($parents, $uid);
 
-            $headers[$idx]->depth = $depth;
-            $headers[$idx]->has_children = $msg_children[$id];
+            $headers[$uid]->depth = $depth;
+            $headers[$uid]->has_children = $msg_children[$uid];
         }
     }
 
@@ -1092,132 +973,114 @@
     /**
      * Private method for listing a set of message headers (search results)
      *
-     * @param   string   $mailbox    Mailbox/folder name
-     * @param   int      $page       Current page to list
-     * @param   string   $sort_field Header field to sort by
-     * @param   string   $sort_order Sort order [ASC|DESC]
-     * @param   int  $slice      Number of slice items to extract from result array
+     * @param   string   $mailbox  Mailbox/folder name
+     * @param   int      $page     Current page to list
+     * @param   int      $slice    Number of slice items to extract from result array
+     *
      * @return  array    Indexed array with message header objects
      * @access  private
-     * @see     rcube_imap::list_header_set()
      */
-    private function _list_header_set($mailbox, $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
+    private function _list_header_set($mailbox, $page, $slice=0)
     {
-        if (!strlen($mailbox) || empty($this->search_set))
+        if (!strlen($mailbox) || empty($this->search_set) || $this->search_set->isEmpty()) {
             return array();
+        }
 
         // use saved messages from searching
-        if ($this->threading)
-            return $this->_list_thread_header_set($mailbox, $page, $sort_field, $sort_order, $slice);
+        if ($this->threading) {
+            return $this->_list_thread_header_set($mailbox, $page, $slice);
+        }
 
         // search set is threaded, we need a new one
         if ($this->search_threads) {
-            if (empty($this->search_set['tree']))
-                return array();
-            $this->search('', $this->search_string, $this->search_charset, $sort_field);
+            $this->search('', $this->search_string, $this->search_charset, $this->sort_field);
         }
 
-        $msgs = $this->search_set;
-        $a_msg_headers = array();
-        $page = $page ? $page : $this->list_page;
-        $start_msg = ($page-1) * $this->page_size;
+        $index = clone $this->search_set;
+        $from  = ($page-1) * $this->page_size;
+        $to    = $from + $this->page_size;
 
-        $this->_set_sort_order($sort_field, $sort_order);
+        // return empty array if no messages found
+        if ($index->isEmpty())
+            return array();
 
         // quickest method (default sorting)
         if (!$this->search_sort_field && !$this->sort_field) {
-            if ($sort_order == 'DESC')
-                $msgs = array_reverse($msgs);
+            $got_index = true;
+        }
+        // sorted messages, so we can first slice array and then fetch only wanted headers
+        else if ($this->search_sorted) { // SORT searching result
+            $got_index = true;
+            // reset search set if sorting field has been changed
+            if ($this->sort_field && $this->search_sort_field != $this->sort_field) {
+                $this->search('', $this->search_string, $this->search_charset, $this->sort_field);
+
+                $index = clone $this->search_set;
+
+                // return empty array if no messages found
+                if ($index->isEmpty())
+                    return array();
+            }
+        }
+
+        if ($got_index) {
+            if ($this->sort_order != $index->getParameters('ORDER')) {
+                $index->revert();
+            }
 
             // get messages uids for one page
-            $msgs = array_slice(array_values($msgs), $start_msg, min(count($msgs)-$start_msg, $this->page_size));
+            $index->slice($from, $to-$from);
 
             if ($slice)
-                $msgs = array_slice($msgs, -$slice, $slice);
+                $index->slice(-$slice, $slice);
 
             // fetch headers
-            $this->_fetch_headers($mailbox, join(',',$msgs), $a_msg_headers, NULL);
-
-            // I didn't found in RFC that FETCH always returns messages sorted by index
-            $sorter = new rcube_header_sorter();
-            $sorter->set_sequence_numbers($msgs);
-            $sorter->sort_headers($a_msg_headers);
+            $a_index       = $index->get();
+            $a_msg_headers = $this->fetch_headers($mailbox, $a_index);
 
             return array_values($a_msg_headers);
         }
 
-        // sorted messages, so we can first slice array and then fetch only wanted headers
-        if ($this->search_sorted) { // SORT searching result
-            // reset search set if sorting field has been changed
-            if ($this->sort_field && $this->search_sort_field != $this->sort_field)
-                $msgs = $this->search('', $this->search_string, $this->search_charset, $this->sort_field);
+        // SEARCH result, need sorting
+        $cnt = $index->count();
+
+        // 300: experimantal value for best result
+        if (($cnt > 300 && $cnt > $this->page_size) || !$this->sort_field) {
+            // use memory less expensive (and quick) method for big result set
+            $index = clone $this->message_index('', $this->sort_field, $this->sort_order);
+            // get messages uids for one page...
+            $index->slice($start_msg, min($cnt-$from, $this->page_size));
+
+            if ($slice)
+                $index->slice(-$slice, $slice);
+
+            // ...and fetch headers
+            $a_index       = $index->get();
+            $a_msg_headers = $this->fetch_headers($mailbox, $a_index);
+
+            return array_values($a_msg_headers);
+        }
+        else {
+            // for small result set we can fetch all messages headers
+            $a_index       = $index->get();
+            $a_msg_headers = $this->fetch_headers($mailbox, $a_index, false);
 
             // return empty array if no messages found
-            if (empty($msgs))
+            if (!is_array($a_msg_headers) || empty($a_msg_headers))
                 return array();
 
-            if ($sort_order == 'DESC')
-                $msgs = array_reverse($msgs);
+            // if not already sorted
+            $a_msg_headers = $this->conn->sortHeaders(
+                $a_msg_headers, $this->sort_field, $this->sort_order);
 
-            // get messages uids for one page
-            $msgs = array_slice(array_values($msgs), $start_msg, min(count($msgs)-$start_msg, $this->page_size));
+            // only return the requested part of the set
+            $a_msg_headers = array_slice(array_values($a_msg_headers),
+                $from, min($cnt-$to, $this->page_size));
 
             if ($slice)
-                $msgs = array_slice($msgs, -$slice, $slice);
+                $a_msg_headers = array_slice($a_msg_headers, -$slice, $slice);
 
-            // fetch headers
-            $this->_fetch_headers($mailbox, join(',',$msgs), $a_msg_headers, NULL);
-
-            $sorter = new rcube_header_sorter();
-            $sorter->set_sequence_numbers($msgs);
-            $sorter->sort_headers($a_msg_headers);
-
-            return array_values($a_msg_headers);
-        }
-        else { // SEARCH result, need sorting
-            $cnt = count($msgs);
-            // 300: experimantal value for best result
-            if (($cnt > 300 && $cnt > $this->page_size) || !$this->sort_field) {
-                // use memory less expensive (and quick) method for big result set
-                $a_index = $this->message_index('', $this->sort_field, $this->sort_order);
-                // get messages uids for one page...
-                $msgs = array_slice($a_index, $start_msg, min($cnt-$start_msg, $this->page_size));
-                if ($slice)
-                    $msgs = array_slice($msgs, -$slice, $slice);
-                // ...and fetch headers
-                $this->_fetch_headers($mailbox, join(',', $msgs), $a_msg_headers, NULL);
-
-                // return empty array if no messages found
-                if (!is_array($a_msg_headers) || empty($a_msg_headers))
-                    return array();
-
-                $sorter = new rcube_header_sorter();
-                $sorter->set_sequence_numbers($msgs);
-                $sorter->sort_headers($a_msg_headers);
-
-                return array_values($a_msg_headers);
-            }
-            else {
-                // for small result set we can fetch all messages headers
-                $this->_fetch_headers($mailbox, join(',', $msgs), $a_msg_headers, NULL);
-
-                // return empty array if no messages found
-                if (!is_array($a_msg_headers) || empty($a_msg_headers))
-                    return array();
-
-                // if not already sorted
-                $a_msg_headers = $this->conn->sortHeaders(
-                    $a_msg_headers, $this->sort_field, $this->sort_order);
-
-                // only return the requested part of the set
-                $a_msg_headers = array_slice(array_values($a_msg_headers),
-                    $start_msg, min($cnt-$start_msg, $this->page_size));
-
-                if ($slice)
-                    $a_msg_headers = array_slice($a_msg_headers, -$slice, $slice);
-
-                return $a_msg_headers;
-            }
+            return $a_msg_headers;
         }
     }
 
@@ -1227,135 +1090,65 @@
      *
      * @param   string   $mailbox    Mailbox/folder name
      * @param   int      $page       Current page to list
-     * @param   string   $sort_field Header field to sort by
-     * @param   string   $sort_order Sort order [ASC|DESC]
      * @param   int      $slice      Number of slice items to extract from result array
+     *
      * @return  array    Indexed array with message header objects
      * @access  private
      * @see     rcube_imap::list_header_set()
      */
-    private function _list_thread_header_set($mailbox, $page=NULL, $sort_field=NULL, $sort_order=NULL, $slice=0)
+    private function _list_thread_header_set($mailbox, $page, $slice=0)
     {
         // update search_set if previous data was fetched with disabled threading
         if (!$this->search_threads) {
-            if (empty($this->search_set))
+            if ($this->search_set->isEmpty())
                 return array();
-            $this->search('', $this->search_string, $this->search_charset, $sort_field);
+            $this->search('', $this->search_string, $this->search_charset, $this->sort_field);
         }
 
-        // empty result
-        if (empty($this->search_set['tree']))
+        return $this->_fetch_thread_headers($mailbox, clone $this->search_set, $page, $slice);
+    }
+
+
+    /**
+     * Fetches messages headers (by UID)
+     *
+     * @param  string  $mailbox  Mailbox name
+     * @param  array   $msgs     Message UIDs
+     * @param  bool    $sort     Enables result sorting by $msgs
+     * @param  bool    $force    Disables cache use
+     *
+     * @return array Messages headers indexed by UID
+     * @access private
+     */
+    function fetch_headers($mailbox, $msgs, $sort = true, $force = false)
+    {
+        if (empty($msgs))
             return array();
 
-        $thread_tree = $this->search_set['tree'];
-        $msg_depth = $this->search_set['depth'];
-        $has_children = $this->search_set['children'];
-        $a_msg_headers = array();
-
-        $page = $page ? $page : $this->list_page;
-        $start_msg = ($page-1) * $this->page_size;
-
-        $this->_set_sort_order($sort_field, $sort_order);
-
-        $msg_index = $this->_sort_threads($mailbox, $thread_tree, array_keys($msg_depth));
-
-        return $this->_fetch_thread_headers($mailbox,
-            $thread_tree, $msg_depth, $has_children, $msg_index, $page, $slice=0);
-    }
-
-
-    /**
-     * Helper function to get first and last index of the requested set
-     *
-     * @param  int     $max  Messages count
-     * @param  mixed   $page Page number to show, or string 'all'
-     * @return array   Array with two values: first index, last index
-     * @access private
-     */
-    private function _get_message_range($max, $page)
-    {
-        $start_msg = ($page-1) * $this->page_size;
-
-        if ($page=='all') {
-            $begin  = 0;
-            $end    = $max;
-        }
-        else if ($this->sort_order=='DESC') {
-            $begin  = $max - $this->page_size - $start_msg;
-            $end    = $max - $start_msg;
+        if (!$force && ($mcache = $this->get_mcache_engine())) {
+            $headers = $mcache->get_messages($mailbox, $msgs);
         }
         else {
-            $begin  = $start_msg;
-            $end    = $start_msg + $this->page_size;
+            // fetch reqested headers from server
+            $headers = $this->conn->fetchHeaders(
+                $mailbox, $msgs, true, false, $this->get_fetch_headers());
         }
 
-        if ($begin < 0) $begin = 0;
-        if ($end < 0) $end = $max;
-        if ($end > $max) $end = $max;
+        if (empty($headers))
+            return array();
 
-        return array($begin, $end);
-    }
-
-
-    /**
-     * Fetches message headers (used for loop)
-     *
-     * @param  string  $mailbox       Mailbox name
-     * @param  string  $msgs          Message index to fetch
-     * @param  array   $a_msg_headers Reference to message headers array
-     * @param  string  $cache_key     Cache index key
-     * @return int     Messages count
-     * @access private
-     */
-    private function _fetch_headers($mailbox, $msgs, &$a_msg_headers, $cache_key)
-    {
-        // fetch reqested headers from server
-        $a_header_index = $this->conn->fetchHeaders(
-            $mailbox, $msgs, false, false, $this->get_fetch_headers());
-
-        if (empty($a_header_index))
-            return 0;
-
-        foreach ($a_header_index as $i => $headers) {
-            $a_msg_headers[$headers->uid] = $headers;
+        foreach ($headers as $h) {
+            $a_msg_headers[$h->uid] = $h;
         }
 
-        // Update cache
-        if ($this->messages_caching && $cache_key) {
-            // cache is incomplete?
-            $cache_index = $this->get_message_cache_index($cache_key);
-
-            foreach ($a_header_index as $headers) {
-                // message in cache
-                if ($cache_index[$headers->id] == $headers->uid) {
-                    unset($cache_index[$headers->id]);
-                    continue;
-                }
-                // wrong UID at this position
-                if ($cache_index[$headers->id]) {
-                    $for_remove[] = $cache_index[$headers->id];
-                    unset($cache_index[$headers->id]);
-                }
-                // message UID in cache but at wrong position
-                if (is_int($key = array_search($headers->uid, $cache_index))) {
-                    $for_remove[] = $cache_index[$key];
-                    unset($cache_index[$key]);
-                }
-
-                $for_create[] = $headers->uid;
-            }
-
-            if ($for_remove)
-                $this->remove_message_cache($cache_key, $for_remove);
-
-            // add messages to cache
-            foreach ((array)$for_create as $uid) {
-                $headers = $a_msg_headers[$uid];
-                $this->add_message_cache($cache_key, $headers->id, $headers, NULL, true);
-            }
+        if ($sort) {
+            // use this class for message sorting
+            $sorter = new rcube_header_sorter();
+            $sorter->set_index($msgs);
+            $sorter->sort_headers($a_msg_headers);
         }
 
-        return count($a_msg_headers);
+        return $a_msg_headers;
     }
 
 
@@ -1368,7 +1161,7 @@
      * @param string $mailbox Mailbox/folder name
      * @return int   Folder status
      */
-    function mailbox_status($mailbox = null)
+    public function mailbox_status($mailbox = null)
     {
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
@@ -1379,6 +1172,11 @@
         $this->_messagecount($mailbox, 'ALL', true);
 
         $result = 0;
+
+        if (empty($old)) {
+            return $result;
+        }
+
         $new = $this->get_folder_stats($mailbox);
 
         // got new messages
@@ -1426,291 +1224,169 @@
 
 
     /**
-     * Return sorted array of message IDs (not UIDs)
+     * Return sorted list of message UIDs
      *
      * @param string $mailbox    Mailbox to get index from
      * @param string $sort_field Sort column
      * @param string $sort_order Sort order [ASC, DESC]
-     * @return array Indexed array with message IDs
+     *
+     * @return rcube_result_index|rcube_result_thread List of messages (UIDs)
      */
-    function message_index($mailbox='', $sort_field=NULL, $sort_order=NULL)
+    public function message_index($mailbox='', $sort_field=NULL, $sort_order=NULL)
     {
         if ($this->threading)
             return $this->thread_index($mailbox, $sort_field, $sort_order);
 
-        $this->_set_sort_order($sort_field, $sort_order);
+        $this->set_sort_order($sort_field, $sort_order);
 
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
         }
-        $key = "{$mailbox}:{$this->sort_field}:{$this->sort_order}:{$this->search_string}.msgi";
 
         // we have a saved search result, get index from there
-        if (!isset($this->icache[$key]) && $this->search_string
-            && !$this->search_threads && $mailbox == $this->mailbox) {
-            // use message index sort as default sorting
-            if (!$this->sort_field) {
-                $msgs = $this->search_set;
-
-                if ($this->search_sort_field != 'date')
-                    sort($msgs);
-
-                if ($this->sort_order == 'DESC')
-                    $this->icache[$key] = array_reverse($msgs);
-                else
-                    $this->icache[$key] = $msgs;
+        if ($this->search_string) {
+            if ($this->search_threads) {
+                $this->search($mailbox, $this->search_string, $this->search_charset, $this->sort_field);
             }
-            // sort with SORT command
-            else if ($this->search_sorted) {
-                if ($this->sort_field && $this->search_sort_field != $this->sort_field)
-                    $this->search('', $this->search_string, $this->search_charset, $this->sort_field);
 
-                if ($this->sort_order == 'DESC')
-                    $this->icache[$key] = array_reverse($this->search_set);
-                else
-                    $this->icache[$key] = $this->search_set;
+            // use message index sort as default sorting
+            if (!$this->sort_field || $this->search_sorted) {
+                if ($this->sort_field && $this->search_sort_field != $this->sort_field) {
+                    $this->search($mailbox, $this->search_string, $this->search_charset, $this->sort_field);
+                }
+                $index = $this->search_set;
             }
             else {
-                $a_index = $this->conn->fetchHeaderIndex($mailbox,
-	                join(',', $this->search_set), $this->sort_field, $this->skip_deleted);
-
-                if (is_array($a_index)) {
-                    if ($this->sort_order=="ASC")
-                        asort($a_index);
-                    else if ($this->sort_order=="DESC")
-                        arsort($a_index);
-
-                    $this->icache[$key] = array_keys($a_index);
-                }
-                else {
-                    $this->icache[$key] = array();
-                }
+                $index = $this->conn->index($mailbox, $this->search_set->get(),
+                    $this->sort_field, $this->skip_deleted, true, true);
             }
-        }
 
-        // have stored it in RAM
-        if (isset($this->icache[$key]))
-            return $this->icache[$key];
+            if ($this->sort_order != $index->getParameters('ORDER')) {
+                $index->revert();
+            }
+
+            return $index;
+        }
 
         // check local cache
-        $cache_key = $mailbox.'.msg';
-        $cache_status = $this->check_cache_status($mailbox, $cache_key);
-
-        // cache is OK
-        if ($cache_status>0) {
-            $a_index = $this->get_message_cache_index($cache_key,
-                $this->sort_field, $this->sort_order);
-            return array_keys($a_index);
+        if ($mcache = $this->get_mcache_engine()) {
+            $index = $mcache->get_index($mailbox, $this->sort_field, $this->sort_order);
+        }
+        // fetch from IMAP server
+        else {
+            $index = $this->message_index_direct(
+                $mailbox, $this->sort_field, $this->sort_order);
         }
 
-        // use message index sort as default sorting
-        if (!$this->sort_field) {
-            if ($this->skip_deleted) {
-                $a_index = $this->_search_index($mailbox, 'ALL');
-            } else if ($max = $this->_messagecount($mailbox)) {
-                $a_index = range(1, $max);
-            }
-
-            if ($a_index !== false && $this->sort_order == 'DESC')
-                $a_index = array_reverse($a_index);
-
-            $this->icache[$key] = $a_index;
-        }
-        // fetch complete message index
-        else if ($this->get_capability('SORT') &&
-            ($a_index = $this->conn->sort($mailbox,
-                $this->sort_field, $this->skip_deleted ? 'UNDELETED' : '')) !== false
-        ) {
-            if ($this->sort_order == 'DESC')
-                $a_index = array_reverse($a_index);
-
-            $this->icache[$key] = $a_index;
-        }
-        else if ($a_index = $this->conn->fetchHeaderIndex(
-            $mailbox, "1:*", $this->sort_field, $this->skip_deleted)) {
-            if ($this->sort_order=="ASC")
-                asort($a_index);
-            else if ($this->sort_order=="DESC")
-                arsort($a_index);
-
-            $this->icache[$key] = array_keys($a_index);
-        }
-
-        return $this->icache[$key] !== false ? $this->icache[$key] : array();
+        return $index;
     }
 
 
     /**
-     * Return sorted array of threaded message IDs (not UIDs)
+     * Return sorted list of message UIDs ignoring current search settings.
+     * Doesn't uses cache by default.
      *
      * @param string $mailbox    Mailbox to get index from
      * @param string $sort_field Sort column
      * @param string $sort_order Sort order [ASC, DESC]
-     * @return array Indexed array with message IDs
+     * @param bool   $skip_cache Disables cache usage
+     *
+     * @return rcube_result_index Sorted list of message UIDs
+     */
+    public function message_index_direct($mailbox, $sort_field = null, $sort_order = null, $skip_cache = true)
+    {
+        if (!$skip_cache && ($mcache = $this->get_mcache_engine())) {
+            $index = $mcache->get_index($mailbox, $sort_field, $sort_order);
+        }
+        // use message index sort as default sorting
+        else if (!$sort_field) {
+            if ($this->skip_deleted && !empty($this->icache['undeleted_idx'])
+                && $this->icache['undeleted_idx']->getParameters('MAILBOX') == $mailbox
+            ) {
+                $index = $this->icache['undeleted_idx'];
+            }
+            else {
+                $index = $this->conn->search($mailbox,
+                    'ALL' .($this->skip_deleted ? ' UNDELETED' : ''), true);
+            }
+        }
+        // fetch complete message index
+        else {
+            if ($this->get_capability('SORT')) {
+                $index = $this->conn->sort($mailbox, $sort_field,
+                    $this->skip_deleted ? 'UNDELETED' : '', true);
+            }
+
+            if (empty($index) || $index->isError()) {
+                $index = $this->conn->index($mailbox, "1:*", $sort_field,
+                    $this->skip_deleted, false, true);
+            }
+        }
+
+        if ($sort_order != $index->getParameters('ORDER')) {
+            $index->revert();
+        }
+
+        return $index;
+    }
+
+
+    /**
+     * Return index of threaded message UIDs
+     *
+     * @param string $mailbox    Mailbox to get index from
+     * @param string $sort_field Sort column
+     * @param string $sort_order Sort order [ASC, DESC]
+     *
+     * @return rcube_result_thread Message UIDs
      */
     function thread_index($mailbox='', $sort_field=NULL, $sort_order=NULL)
     {
-        $this->_set_sort_order($sort_field, $sort_order);
-
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
         }
-        $key = "{$mailbox}:{$this->sort_field}:{$this->sort_order}:{$this->search_string}.thi";
 
         // we have a saved search result, get index from there
-        if (!isset($this->icache[$key]) && $this->search_string
-            && $this->search_threads && $mailbox == $this->mailbox) {
-            // use message IDs for better performance
-            $ids = array_keys_recursive($this->search_set['tree']);
-            $this->icache[$key] = $this->_flatten_threads($mailbox, $this->search_set['tree'], $ids);
+        if ($this->search_string && $this->search_threads && $mailbox == $this->mailbox) {
+            $threads = $this->search_set;
+        }
+        else {
+            // get all threads (default sort order)
+            $threads = $this->fetch_threads($mailbox);
         }
 
-        // have stored it in RAM
-        if (isset($this->icache[$key]))
-            return $this->icache[$key];
-/*
-        // check local cache
-        $cache_key = $mailbox.'.msg';
-        $cache_status = $this->check_cache_status($mailbox, $cache_key);
+        $this->set_sort_order($sort_field, $sort_order);
+        $this->sort_threads($threads);
 
-        // cache is OK
-        if ($cache_status>0) {
-            $a_index = $this->get_message_cache_index($cache_key, $this->sort_field, $this->sort_order);
-            return array_keys($a_index);
-        }
-*/
-        // get all threads (default sort order)
-        list ($thread_tree) = $this->_fetch_threads($mailbox);
-
-        $this->icache[$key] = $this->_flatten_threads($mailbox, $thread_tree);
-
-        return $this->icache[$key];
+        return $threads;
     }
 
 
     /**
-     * Return array of threaded messages (all, not only roots)
+     * Sort threaded result, using THREAD=REFS method
      *
-     * @param string $mailbox     Mailbox to get index from
-     * @param array  $thread_tree Threaded messages array (see _fetch_threads())
-     * @param array  $ids         Message IDs if we know what we need (e.g. search result)
-     *                            for better performance
-     * @return array Indexed array with message IDs
-     *
-     * @access private
+     * @param rcube_result_thread $threads  Threads result set
      */
-    private function _flatten_threads($mailbox, $thread_tree, $ids=null)
+    private function sort_threads($threads)
     {
-        if (empty($thread_tree))
-            return array();
-
-        $msg_index = $this->_sort_threads($mailbox, $thread_tree, $ids);
-
-        if ($this->sort_order == 'DESC')
-            $msg_index = array_reverse($msg_index);
-
-        // flatten threads array
-        $all_ids = array();
-        foreach ($msg_index as $root) {
-            $all_ids[] = $root;
-            if (!empty($thread_tree[$root])) {
-                foreach (array_keys_recursive($thread_tree[$root]) as $val)
-                    $all_ids[] = $val;
-            }
-        }
-
-        return $all_ids;
-    }
-
-
-    /**
-     * @param string $mailbox Mailbox name
-     * @access private
-     */
-    private function sync_header_index($mailbox)
-    {
-        $cache_key = $mailbox.'.msg';
-        $cache_index = $this->get_message_cache_index($cache_key);
-        $chunk_size = 1000;
-
-        // cache is empty, get all messages
-        if (is_array($cache_index) && empty($cache_index)) {
-            $max = $this->_messagecount($mailbox);
-            // syncing a big folder maybe slow
-            @set_time_limit(0);
-            $start = 1;
-            $end   = min($chunk_size, $max);
-            while (true) {
-                // do this in loop to save memory (1000 msgs ~= 10 MB)
-                if ($headers = $this->conn->fetchHeaders($mailbox,
-                    "$start:$end", false, false, $this->get_fetch_headers())
-                ) {
-                    foreach ($headers as $header) {
-                        $this->add_message_cache($cache_key, $header->id, $header, NULL, true);
-                    }
-                }
-                if ($end - $start < $chunk_size - 1)
-                    break;
-
-                $end   = min($end+$chunk_size, $max);
-                $start += $chunk_size;
-            }
+        if ($threads->isEmpty()) {
             return;
         }
 
-        // fetch complete message index
-        if (isset($this->icache['folder_index']))
-            $a_message_index = &$this->icache['folder_index'];
-        else
-            $a_message_index = $this->conn->fetchHeaderIndex($mailbox, "1:*", 'UID', $this->skip_deleted);
+        // THREAD=ORDEREDSUBJECT: sorting by sent date of root message
+        // THREAD=REFERENCES:     sorting by sent date of root message
+        // THREAD=REFS:           sorting by the most recent date in each thread
 
-        if ($a_message_index === false || $cache_index === null)
-            return;
+        if ($this->sort_field && ($this->sort_field != 'date' || $this->get_capability('THREAD') != 'REFS')) {
+            $index = $this->message_index_direct($this->mailbox, $this->sort_field, $this->sort_order, false);
 
-        // compare cache index with real index
-        foreach ($a_message_index as $id => $uid) {
-            // message in cache at correct position
-            if ($cache_index[$id] == $uid) {
-                unset($cache_index[$id]);
-                continue;
+            if (!$index->isEmpty()) {
+                $threads->sort($index);
             }
-
-            // other message at this position
-            if (isset($cache_index[$id])) {
-                $for_remove[] = $cache_index[$id];
-                unset($cache_index[$id]);
-            }
-
-            // message in cache but at wrong position
-            if (is_int($key = array_search($uid, $cache_index))) {
-                $for_remove[] = $uid;
-                unset($cache_index[$key]);
-            }
-
-            $for_update[] = $id;
         }
-
-        // remove messages at wrong positions and those deleted that are still in cache_index
-        if (!empty($for_remove))
-            $cache_index = array_merge($cache_index, $for_remove);
-
-        if (!empty($cache_index))
-            $this->remove_message_cache($cache_key, $cache_index);
-
-        // fetch complete headers and add to cache
-        if (!empty($for_update)) {
-            // syncing a big folder maybe slow
-            @set_time_limit(0);
-            // To save memory do this in chunks
-            $for_update = array_chunk($for_update, $chunk_size);
-            foreach ($for_update as $uids) {
-                if ($headers = $this->conn->fetchHeaders($mailbox,
-                    $uids, false, false, $this->get_fetch_headers())
-                ) {
-                    foreach ($headers as $header) {
-                        $this->add_message_cache($cache_key, $header->id, $header, NULL, true);
-                    }
-                }
+        else {
+            if ($this->sort_order != $threads->getParameters('ORDER')) {
+                $threads->revert();
             }
         }
     }
@@ -1723,13 +1399,13 @@
      * @param  string  $str        Search criteria
      * @param  string  $charset    Search charset
      * @param  string  $sort_field Header field to sort by
-     * @return array   search results as list of message IDs
      * @access public
+     * @todo: Search criteria should be provided in non-IMAP format, eg. array
      */
-    function search($mailbox='', $str=NULL, $charset=NULL, $sort_field=NULL)
+    function search($mailbox='', $str='ALL', $charset=NULL, $sort_field=NULL)
     {
         if (!$str)
-            return false;
+            $str = 'ALL';
 
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
@@ -1737,10 +1413,8 @@
 
         $results = $this->_search_index($mailbox, $str, $charset, $sort_field);
 
-        $this->set_search_set($str, $results, $charset, $sort_field, (bool)$this->threading,
+        $this->set_search_set($str, $results, $charset, $sort_field,
             $this->threading || $this->search_sorted ? true : false);
-
-        return $results;
     }
 
 
@@ -1751,8 +1425,8 @@
      * @param string $criteria   Search criteria
      * @param string $charset    Charset
      * @param string $sort_field Sorting field
-     * @return array   search results as list of message ids
-     * @access private
+     *
+     * @return rcube_result_index|rcube_result_thread  Search results (UIDs)
      * @see rcube_imap::search()
      */
     private function _search_index($mailbox, $criteria='ALL', $charset=NULL, $sort_field=NULL)
@@ -1763,63 +1437,44 @@
             $criteria = 'UNDELETED '.$criteria;
 
         if ($this->threading) {
-            $a_messages = $this->conn->thread($mailbox, $this->threading, $criteria, $charset);
+            $threads = $this->conn->thread($mailbox, $this->threading, $criteria, true, $charset);
 
             // Error, try with US-ASCII (RFC5256: SORT/THREAD must support US-ASCII and UTF-8,
             // but I've seen that Courier doesn't support UTF-8)
-            if ($a_messages === false && $charset && $charset != 'US-ASCII')
-                $a_messages = $this->conn->thread($mailbox, $this->threading,
-                    $this->convert_criteria($criteria, $charset), 'US-ASCII');
+            if ($threads->isError() && $charset && $charset != 'US-ASCII')
+                $threads = $this->conn->thread($mailbox, $this->threading,
+                    $this->convert_criteria($criteria, $charset), true, 'US-ASCII');
 
-            if ($a_messages !== false) {
-                list ($thread_tree, $msg_depth, $has_children) = $a_messages;
-                $a_messages = array(
-                    'tree' 	=> $thread_tree,
-	                'depth'	=> $msg_depth,
-	                'children' => $has_children
-                );
-            }
-
-            return $a_messages;
+            return $threads;
         }
 
         if ($sort_field && $this->get_capability('SORT')) {
-            $charset = $charset ? $charset : $this->default_charset;
-            $a_messages = $this->conn->sort($mailbox, $sort_field, $criteria, false, $charset);
+            $charset  = $charset ? $charset : $this->default_charset;
+            $messages = $this->conn->sort($mailbox, $sort_field, $criteria, true, $charset);
 
             // Error, try with US-ASCII (RFC5256: SORT/THREAD must support US-ASCII and UTF-8,
-            // but I've seen that Courier doesn't support UTF-8)
-            if ($a_messages === false && $charset && $charset != 'US-ASCII')
-                $a_messages = $this->conn->sort($mailbox, $sort_field,
-                    $this->convert_criteria($criteria, $charset), false, 'US-ASCII');
+            // but I've seen Courier with disabled UTF-8 support)
+            if ($messages->isError() && $charset && $charset != 'US-ASCII')
+                $messages = $this->conn->sort($mailbox, $sort_field,
+                    $this->convert_criteria($criteria, $charset), true, 'US-ASCII');
 
-            if ($a_messages !== false) {
+            if (!$messages->isError()) {
                 $this->search_sorted = true;
-                return $a_messages;
+                return $messages;
             }
         }
 
-        if ($orig_criteria == 'ALL') {
-            $max = $this->_messagecount($mailbox);
-            $a_messages = $max ? range(1, $max) : array();
-        }
-        else {
-            $a_messages = $this->conn->search($mailbox,
-                ($charset ? "CHARSET $charset " : '') . $criteria);
+        $messages = $this->conn->search($mailbox,
+            ($charset ? "CHARSET $charset " : '') . $criteria, true);
 
-            // Error, try with US-ASCII (some servers may support only US-ASCII)
-            if ($a_messages === false && $charset && $charset != 'US-ASCII')
-                $a_messages = $this->conn->search($mailbox,
-                    'CHARSET US-ASCII ' . $this->convert_criteria($criteria, $charset));
-
-            // I didn't found that SEARCH should return sorted IDs
-            if (is_array($a_messages) && !$this->sort_field)
-                sort($a_messages);
-        }
+        // Error, try with US-ASCII (some servers may support only US-ASCII)
+        if ($messages->isError() && $charset && $charset != 'US-ASCII')
+            $messages = $this->conn->search($mailbox,
+                $this->convert_criteria($criteria, $charset), true);
 
         $this->search_sorted = false;
 
-        return $a_messages;
+        return $messages;
     }
 
 
@@ -1830,19 +1485,21 @@
      * @param  string  $mailbox Mailbox name to search in
      * @param  string  $str     Search string
      * @param  boolean $ret_uid True if UIDs should be returned
-     * @return array   Search results as list of message IDs or UIDs
-     * @access public
+     *
+     * @return rcube_result_index  Search result (UIDs)
      */
-    function search_once($mailbox='', $str=NULL, $ret_uid=false)
+    function search_once($mailbox='', $str='ALL')
     {
         if (!$str)
-            return false;
+            return 'ALL';
 
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
         }
 
-        return $this->conn->search($mailbox, $str, $ret_uid);
+        $index = $this->conn->search($mailbox, $str, true);
+
+        return $index;
     }
 
 
@@ -1864,9 +1521,9 @@
                 $string_offset = $m[1] + strlen($m[0]) + 4; // {}\r\n
                 $string = substr($str, $string_offset - 1, $m[0]);
                 $string = rcube_charset_convert($string, $charset, $dest_charset);
-                if (!$string)
+                if ($string === false)
                     continue;
-                $res .= sprintf("%s{%d}\r\n%s", substr($str, $last, $m[1] - $last - 1), strlen($string), $string);
+                $res .= substr($str, $last, $m[1] - $last - 1) . rcube_imap_generic::escape($string);
                 $last = $m[0] + $string_offset - 1;
             }
             if ($last < strlen($str))
@@ -1880,161 +1537,58 @@
 
 
     /**
-     * Sort thread
-     *
-     * @param string $mailbox     Mailbox name
-     * @param  array $thread_tree Unsorted thread tree (rcube_imap_generic::thread() result)
-     * @param  array $ids         Message IDs if we know what we need (e.g. search result)
-     * @return array Sorted roots IDs
-     * @access private
-     */
-    private function _sort_threads($mailbox, $thread_tree, $ids=NULL)
-    {
-        // THREAD=ORDEREDSUBJECT: 	sorting by sent date of root message
-        // THREAD=REFERENCES: 	sorting by sent date of root message
-        // THREAD=REFS: 		sorting by the most recent date in each thread
-        // default sorting
-        if (!$this->sort_field || ($this->sort_field == 'date' && $this->threading == 'REFS')) {
-            return array_keys((array)$thread_tree);
-          }
-        // here we'll implement REFS sorting, for performance reason
-        else { // ($sort_field == 'date' && $this->threading != 'REFS')
-            // use SORT command
-            if ($this->get_capability('SORT') && 
-                ($a_index = $this->conn->sort($mailbox, $this->sort_field,
-	                !empty($ids) ? $ids : ($this->skip_deleted ? 'UNDELETED' : ''))) !== false
-            ) {
-	            // return unsorted tree if we've got no index data
-	            if (!$a_index)
-	                return array_keys((array)$thread_tree);
-            }
-            else {
-                // fetch specified headers for all messages and sort them
-                $a_index = $this->conn->fetchHeaderIndex($mailbox, !empty($ids) ? $ids : "1:*",
-	                $this->sort_field, $this->skip_deleted);
-
-	            // return unsorted tree if we've got no index data
-	            if (!$a_index)
-	                return array_keys((array)$thread_tree);
-
-                asort($a_index); // ASC
-	            $a_index = array_values($a_index);
-            }
-
-	        return $this->_sort_thread_refs($thread_tree, $a_index);
-        }
-    }
-
-
-    /**
-     * THREAD=REFS sorting implementation
-     *
-     * @param  array $tree  Thread tree array (message identifiers as keys)
-     * @param  array $index Array of sorted message identifiers
-     * @return array   Array of sorted roots messages
-     * @access private
-     */
-    private function _sort_thread_refs($tree, $index)
-    {
-        if (empty($tree))
-            return array();
-
-        $index = array_combine(array_values($index), $index);
-
-        // assign roots
-        foreach ($tree as $idx => $val) {
-            $index[$idx] = $idx;
-            if (!empty($val)) {
-                $idx_arr = array_keys_recursive($tree[$idx]);
-                foreach ($idx_arr as $subidx)
-                    $index[$subidx] = $idx;
-            }
-        }
-
-        $index = array_values($index);
-
-        // create sorted array of roots
-        $msg_index = array();
-        if ($this->sort_order != 'DESC') {
-            foreach ($index as $idx)
-                if (!isset($msg_index[$idx]))
-                    $msg_index[$idx] = $idx;
-            $msg_index = array_values($msg_index);
-        }
-        else {
-            for ($x=count($index)-1; $x>=0; $x--)
-                if (!isset($msg_index[$index[$x]]))
-                    $msg_index[$index[$x]] = $index[$x];
-            $msg_index = array_reverse($msg_index);
-        }
-
-        return $msg_index;
-    }
-
-
-    /**
      * Refresh saved search set
      *
      * @return array Current search set
      */
     function refresh_search()
     {
-        if (!empty($this->search_string))
-            $this->search_set = $this->search('', $this->search_string, $this->search_charset,
-    	        $this->search_sort_field, $this->search_threads, $this->search_sorted);
+        if (!empty($this->search_string)) {
+            $this->search('', $this->search_string, $this->search_charset, $this->search_sort_field);
+        }
 
         return $this->get_search_set();
     }
 
 
     /**
-     * Check if the given message ID is part of the current search set
+     * Check if the given message UID is part of the current search set
      *
-     * @param string $msgid Message id
+     * @param string $msgid Message UID
+     *
      * @return boolean True on match or if no search request is stored
      */
-    function in_searchset($msgid)
+    function in_searchset($uid)
     {
         if (!empty($this->search_string)) {
-            if ($this->search_threads)
-                return isset($this->search_set['depth']["$msgid"]);
-            else
-                return in_array("$msgid", (array)$this->search_set, true);
+            return $this->search_set->exists($uid);
         }
-        else
-            return true;
+        return true;
     }
 
 
     /**
      * Return message headers object of a specific message
      *
-     * @param int     $id       Message ID
+     * @param int     $id       Message sequence ID or UID
      * @param string  $mailbox  Mailbox to read from
-     * @param boolean $is_uid   True if $id is the message UID
-     * @param boolean $bodystr  True if we need also BODYSTRUCTURE in headers
-     * @return object Message headers representation
+     * @param bool    $force    True to skip cache
+     *
+     * @return rcube_mail_header Message headers
      */
-    function get_headers($id, $mailbox=null, $is_uid=true, $bodystr=false)
+    function get_headers($uid, $mailbox = null, $force = false)
     {
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
         }
-        $uid = $is_uid ? $id : $this->_id2uid($id, $mailbox);
 
         // get cached headers
-        if ($uid && ($headers = &$this->get_cached_message($mailbox.'.msg', $uid)))
-            return $headers;
-
-        $headers = $this->conn->fetchHeader(
-            $mailbox, $id, $is_uid, $bodystr, $this->get_fetch_headers());
-
-        // write headers cache
-        if ($headers) {
-            if ($headers->uid && $headers->id)
-                $this->uid_id_map[$mailbox][$headers->uid] = $headers->id;
-
-            $this->add_message_cache($mailbox.'.msg', $headers->id, $headers, NULL, false, true);
+        if (!$force && $uid && ($mcache = $this->get_mcache_engine())) {
+            $headers = $mcache->get_message($mailbox, $uid);
+        }
+        else {
+            $headers = $this->conn->fetchHeader(
+                $mailbox, $uid, true, true, $this->get_fetch_headers());
         }
 
         return $headers;
@@ -2042,33 +1596,47 @@
 
 
     /**
-     * Fetch body structure from the IMAP server and build
+     * Fetch message headers and body structure from the IMAP server and build
      * an object structure similar to the one generated by PEAR::Mail_mimeDecode
      *
-     * @param int    $uid           Message UID to fetch
-     * @param string $structure_str Message BODYSTRUCTURE string (optional)
-     * @return object rcube_message_part Message part tree or False on failure
+     * @param int     $uid      Message UID to fetch
+     * @param string  $mailbox  Mailbox to read from
+     *
+     * @return object rcube_mail_header Message data
      */
-    function &get_structure($uid, $structure_str='')
+    function get_message($uid, $mailbox = null)
     {
-        $cache_key = $this->mailbox.'.msg';
-        $headers = &$this->get_cached_message($cache_key, $uid);
-
-        // return cached message structure
-        if (is_object($headers) && is_object($headers->structure)) {
-            return $headers->structure;
+        if (!strlen($mailbox)) {
+            $mailbox = $this->mailbox;
         }
 
-        if (!$structure_str) {
-            $structure_str = $this->conn->fetchStructureString($this->mailbox, $uid, true);
+        // Check internal cache
+        if (!empty($this->icache['message'])) {
+            if (($headers = $this->icache['message']) && $headers->uid == $uid) {
+                return $headers;
+            }
         }
-        $structure = rcube_mime_struct::parseStructure($structure_str);
-        $struct = false;
 
-        // parse structure and add headers
-        if (!empty($structure)) {
-            $headers = $this->get_headers($uid);
-            $this->_msg_id = $headers->id;
+        $headers = $this->get_headers($uid, $mailbox);
+
+        // message doesn't exist?
+        if (empty($headers))
+            return null;
+
+        // structure might be cached
+        if (!empty($headers->structure))
+            return $headers;
+
+        $this->_msg_uid = $uid;
+
+        if (empty($headers->bodystructure)) {
+            $headers->bodystructure = $this->conn->getStructure($mailbox, $uid, true);
+        }
+
+        $structure = $headers->bodystructure;
+
+        if (empty($structure))
+            return $headers;
 
         // set message charset from message headers
         if ($headers->charset)
@@ -2091,26 +1659,21 @@
                 $structure[1] = $m[2];
             }
             else
-                return false;
+                return $headers;
         }
 
         $struct = &$this->_structure_part($structure, 0, '', $headers);
-        $struct->headers = get_object_vars($headers);
 
         // don't trust given content-type
-        if (empty($struct->parts) && !empty($struct->headers['ctype'])) {
+        if (empty($struct->parts) && !empty($headers->ctype)) {
             $struct->mime_id = '1';
-            $struct->mimetype = strtolower($struct->headers['ctype']);
+            $struct->mimetype = strtolower($headers->ctype);
             list($struct->ctype_primary, $struct->ctype_secondary) = explode('/', $struct->mimetype);
         }
 
-        // write structure to cache
-        if ($this->messages_caching)
-            $this->add_message_cache($cache_key, $this->_msg_id, $headers, $struct,
-                $this->icache['message.id'][$uid], true);
-        }
+        $headers->structure = $struct;
 
-        return $struct;
+        return $this->icache['message'] = $headers;
     }
 
 
@@ -2164,7 +1727,7 @@
                     if (strtolower($part[$i][0]) == 'message' && strtolower($part[$i][1]) == 'rfc822') {
                         $mime_part_headers[] = $tmp_part_id;
                     }
-                    else if (in_array('name', (array)$part[$i][2]) && (empty($part[$i][3]) || $part[$i][3]=='NIL')) {
+                    else if (in_array('name', (array)$part[$i][2]) && empty($part[$i][3])) {
                         $mime_part_headers[] = $tmp_part_id;
                     }
                 }
@@ -2175,7 +1738,7 @@
             // headers for parts on all levels
             if ($mime_part_headers) {
                 $mime_part_headers = $this->conn->fetchMIMEHeaders($this->mailbox,
-                    $this->_msg_id, $mime_part_headers);
+                    $this->_msg_uid, $mime_part_headers);
             }
 
             $struct->parts = array();
@@ -2232,13 +1795,13 @@
         }
 
         // read content encoding
-        if (!empty($part[5]) && $part[5]!='NIL') {
+        if (!empty($part[5])) {
             $struct->encoding = strtolower($part[5]);
             $struct->headers['content-transfer-encoding'] = $struct->encoding;
         }
 
         // get part size
-        if (!empty($part[6]) && $part[6]!='NIL')
+        if (!empty($part[6]))
             $struct->size = intval($part[6]);
 
         // read part disposition
@@ -2265,7 +1828,7 @@
         }
 
         // get part ID
-        if (!empty($part[3]) && $part[3]!='NIL') {
+        if (!empty($part[3])) {
             $struct->content_id = $part[3];
             $struct->headers['content-id'] = $part[3];
 
@@ -2277,7 +1840,7 @@
         if ($struct->ctype_primary == 'message' || ($struct->ctype_parameters['name'] && !$struct->content_id)) {
             if (empty($mime_headers)) {
                 $mime_headers = $this->conn->fetchPartHeader(
-                    $this->mailbox, $this->_msg_id, false, $struct->mime_id);
+                    $this->mailbox, $this->_msg_uid, true, $struct->mime_id);
             }
 
             if (is_string($mime_headers))
@@ -2340,7 +1903,7 @@
             if ($i<2) {
                 if (!$headers) {
                     $headers = $this->conn->fetchPartHeader(
-                        $this->mailbox, $this->_msg_id, false, $part->mime_id);
+                        $this->mailbox, $this->_msg_uid, true, $part->mime_id);
                 }
                 $filename_mime = '';
                 $i = 0;
@@ -2359,7 +1922,7 @@
             if ($i<2) {
                 if (!$headers) {
                     $headers = $this->conn->fetchPartHeader(
-                            $this->mailbox, $this->_msg_id, false, $part->mime_id);
+                            $this->mailbox, $this->_msg_uid, true, $part->mime_id);
                 }
                 $filename_encoded = '';
                 $i = 0; $matches = array();
@@ -2378,7 +1941,7 @@
             if ($i<2) {
                 if (!$headers) {
                     $headers = $this->conn->fetchPartHeader(
-                        $this->mailbox, $this->_msg_id, false, $part->mime_id);
+                        $this->mailbox, $this->_msg_uid, true, $part->mime_id);
                 }
                 $filename_mime = '';
                 $i = 0; $matches = array();
@@ -2397,7 +1960,7 @@
             if ($i<2) {
                 if (!$headers) {
                     $headers = $this->conn->fetchPartHeader(
-                        $this->mailbox, $this->_msg_id, false, $part->mime_id);
+                        $this->mailbox, $this->_msg_uid, true, $part->mime_id);
                 }
                 $filename_encoded = '';
                 $i = 0; $matches = array();
@@ -2418,9 +1981,14 @@
 
         // decode filename
         if (!empty($filename_mime)) {
-            $part->filename = rcube_imap::decode_mime_string($filename_mime,
-                $part->charset ? $part->charset : ($this->struct_charset ? $this->struct_charset :
-                rc_detect_encoding($filename_mime, $this->default_charset)));
+            if (!empty($part->charset))
+                $charset = $part->charset;
+            else if (!empty($this->struct_charset))
+                $charset = $this->struct_charset;
+            else
+                $charset = rc_detect_encoding($filename_mime, $this->default_charset);
+
+            $part->filename = rcube_imap::decode_mime_string($filename_mime, $charset);
         }
         else if (!empty($filename_encoded)) {
             // decode filename according to RFC 2231, Section 4
@@ -2428,6 +1996,7 @@
                 $filename_charset = $fmatches[1];
                 $filename_encoded = $fmatches[2];
             }
+
             $part->filename = rcube_charset_convert(urldecode($filename_encoded), $filename_charset);
         }
     }
@@ -2464,42 +2033,44 @@
      */
     function &get_message_part($uid, $part=1, $o_part=NULL, $print=NULL, $fp=NULL, $skip_charset_conv=false)
     {
-        // get part encoding if not provided
+        // get part data if not provided
         if (!is_object($o_part)) {
-            $structure_str = $this->conn->fetchStructureString($this->mailbox, $uid, true);
-            $structure = new rcube_mime_struct();
-            // error or message not found
-            if (!$structure->loadStructure($structure_str)) {
-                return false;
-            }
+            $structure = $this->conn->getStructure($this->mailbox, $uid, true);
+            $part_data = rcube_imap_generic::getStructurePartData($structure, $part);
 
             $o_part = new rcube_message_part;
-            $o_part->ctype_primary = strtolower($structure->getPartType($part));
-            $o_part->encoding      = strtolower($structure->getPartEncoding($part));
-            $o_part->charset       = $structure->getPartCharset($part);
+            $o_part->ctype_primary = $part_data['type'];
+            $o_part->encoding      = $part_data['encoding'];
+            $o_part->charset       = $part_data['charset'];
+            $o_part->size          = $part_data['size'];
         }
 
-        // TODO: Add caching for message parts
-
-        if (!$part) {
-            $part = 'TEXT';
+        if ($o_part && $o_part->size) {
+            $body = $this->conn->handlePartBody($this->mailbox, $uid, true,
+                $part ? $part : 'TEXT', $o_part->encoding, $print, $fp);
         }
-
-        $body = $this->conn->handlePartBody($this->mailbox, $uid, true, $part,
-            $o_part->encoding, $print, $fp);
 
         if ($fp || $print) {
             return true;
         }
 
         // convert charset (if text or message part)
-        if ($body && !$skip_charset_conv &&
-            preg_match('/^(text|message)$/', $o_part->ctype_primary)
-        ) {
-            if (!$o_part->charset || strtoupper($o_part->charset) == 'US-ASCII') {
-                $o_part->charset = $this->default_charset;
+        if ($body && preg_match('/^(text|message)$/', $o_part->ctype_primary)) {
+            // Remove NULL characters if any (#1486189)
+            if (strpos($body, "\x00") !== false) {
+                $body = str_replace("\x00", '', $body);
             }
-            $body = rcube_charset_convert($body, $o_part->charset);
+
+            if (!$skip_charset_conv) {
+                if (!$o_part->charset || strtoupper($o_part->charset) == 'US-ASCII') {
+                    // try to extract charset information from HTML meta tag (#1488125)
+                    if ($o_part->ctype_secondary == 'html' && preg_match('/<meta[^>]+charset=([a-z0-9-_]+)/i', $body, $m))
+                        $o_part->charset = strtoupper($m[1]);
+                    else
+                        $o_part->charset = $this->default_charset;
+                }
+                $body = rcube_charset_convert($body, $o_part->charset);
+            }
         }
 
         return $body;
@@ -2585,12 +2156,12 @@
 
         if ($result) {
             // reload message headers if cached
-            if ($this->messages_caching && !$skip_cache) {
-                $cache_key = $mailbox.'.msg';
-                if ($all_mode)
-                    $this->clear_message_cache($cache_key);
-                else
-                    $this->remove_message_cache($cache_key, explode(',', $uids));
+            // @TODO: update flags instead removing from cache
+            if (!$skip_cache && ($mcache = $this->get_mcache_engine())) {
+                $status = strpos($flag, 'UN') !== 0;
+                $mflag  = preg_replace('/^UN/', '', $flag);
+                $mcache->change_flag($mailbox, $all_mode ? null : explode(',', $uids),
+                    $mflag, $status);
             }
 
             // clear cached counters
@@ -2631,7 +2202,7 @@
      * @param string  $headers Headers string if $message contains only the body
      * @param boolean $is_file True if $message is a filename
      *
-     * @return boolean True on success, False on error
+     * @return int|bool Appended message UID or True on success, False on error
      */
     function save_message($mailbox, &$message, $headers='', $is_file=false)
     {
@@ -2682,10 +2253,14 @@
 
         // make sure mailbox exists
         if ($to_mbox != 'INBOX' && !$this->mailbox_exists($to_mbox)) {
-            if (in_array($to_mbox, $this->default_folders))
-                $this->create_mailbox($to_mbox, true);
-            else
+            if (in_array($to_mbox, $this->default_folders)) {
+                if (!$this->create_mailbox($to_mbox, true)) {
+                    return false;
+                }
+            }
+            else {
                 return false;
+            }
         }
 
         $config = rcmail::get_instance()->config;
@@ -2721,20 +2296,13 @@
                 // threads are too complicated to just remove messages from set
                 if ($this->search_threads || $all_mode)
                     $this->refresh_search();
-                else {
-                    $uids = explode(',', $uids);
-                    foreach ($uids as $uid)
-                        $a_mids[] = $this->_uid2id($uid, $from_mbox);
-                    $this->search_set = array_diff($this->search_set, $a_mids);
-                }
+                else
+                    $this->search_set->filter(explode(',', $uids));
             }
 
-            // update cached message headers
-            $cache_key = $from_mbox.'.msg';
-            if ($all_mode || ($start_index = $this->get_message_cache_index_min($cache_key, $uids))) {
-                // clear cache from the lowest index on
-                $this->clear_message_cache($cache_key, $all_mode ? 1 : $start_index);
-            }
+            // remove cached messages
+            // @TODO: do cache update instead of clearing it
+            $this->clear_message_cache($from_mbox, $all_mode ? null : explode(',', $uids));
         }
 
         return $moved;
@@ -2764,10 +2332,14 @@
 
         // make sure mailbox exists
         if ($to_mbox != 'INBOX' && !$this->mailbox_exists($to_mbox)) {
-            if (in_array($to_mbox, $this->default_folders))
-                $this->create_mailbox($to_mbox, true);
-            else
+            if (in_array($to_mbox, $this->default_folders)) {
+                if (!$this->create_mailbox($to_mbox, true)) {
+                    return false;
+                }
+            }
+            else {
                 return false;
+            }
         }
 
         // copy messages
@@ -2801,7 +2373,7 @@
         if (empty($uids))
             return false;
 
-        $deleted = $this->conn->delete($mailbox, $uids);
+        $deleted = $this->conn->flag($mailbox, $uids, 'DELETED');
 
         if ($deleted) {
             // send expunge command in order to have the deleted message
@@ -2818,20 +2390,12 @@
                 // threads are too complicated to just remove messages from set
                 if ($this->search_threads || $all_mode)
                     $this->refresh_search();
-                else {
-                    $uids = explode(',', $uids);
-                    foreach ($uids as $uid)
-                        $a_mids[] = $this->_uid2id($uid, $mailbox);
-                    $this->search_set = array_diff($this->search_set, $a_mids);
-                }
+                else
+                    $this->search_set->filter(explode(',', $uids));
             }
 
-            // remove deleted messages from cache
-            $cache_key = $mailbox.'.msg';
-            if ($all_mode || ($start_index = $this->get_message_cache_index_min($cache_key, $uids))) {
-                // clear cache from the lowest index on
-                $this->clear_message_cache($cache_key, $all_mode ? 1 : $start_index);
-            }
+            // remove cached messages
+            $this->clear_message_cache($mailbox, $all_mode ? null : explode(',', $uids));
         }
 
         return $deleted;
@@ -2856,9 +2420,9 @@
             $cleared = $this->conn->clearFolder($mailbox);
         }
 
-        // make sure the message count cache is cleared as well
+        // make sure the cache is cleared as well
         if ($cleared) {
-            $this->clear_message_cache($mailbox.'.msg');
+            $this->clear_message_cache($mailbox);
             $a_mailbox_cache = $this->get_cache('messagecount');
             unset($a_mailbox_cache[$mailbox]);
             $this->update_cache('messagecount', $a_mailbox_cache);
@@ -2899,9 +2463,9 @@
     private function _expunge($mailbox, $clear_cache=true, $uids=NULL)
     {
         if ($uids && $this->get_capability('UIDPLUS'))
-            $a_uids = is_array($uids) ? join(',', $uids) : $uids;
+            list($uids, $all_mode) = $this->_parse_uids($uids, $mailbox);
         else
-            $a_uids = NULL;
+            $uids = null;
 
         // force mailbox selection and check if mailbox is writeable
         // to prevent a situation when CLOSE is executed on closed
@@ -2916,13 +2480,13 @@
         }
 
         // CLOSE(+SELECT) should be faster than EXPUNGE
-        if (empty($a_uids) || $a_uids == '1:*')
+        if (empty($uids) || $all_mode)
             $result = $this->conn->close();
         else
-            $result = $this->conn->expunge($mailbox, $a_uids);
+            $result = $this->conn->expunge($mailbox, $uids);
 
         if ($result && $clear_cache) {
-            $this->clear_message_cache($mailbox.'.msg');
+            $this->clear_message_cache($mailbox, $all_mode ? null : explode(',', $uids));
             $this->_clear_messagecount($mailbox);
         }
 
@@ -2946,19 +2510,8 @@
                 $all = true;
             }
             // get UIDs from current search set
-            // @TODO: skip fetchUIDs() and work with IDs instead of UIDs (?)
             else {
-                if ($this->search_threads)
-                    $uids = $this->conn->fetchUIDs($mailbox, array_keys($this->search_set['depth']));
-                else
-                    $uids = $this->conn->fetchUIDs($mailbox, $this->search_set);
-
-                // save ID-to-UID mapping in local cache
-                if (is_array($uids))
-                    foreach ($uids as $id => $uid)
-                        $this->uid_id_map[$mailbox][$uid] = $id;
-
-                $uids = join(',', $uids);
+                $uids = join(',', $this->search_set->get());
             }
         }
         else {
@@ -2973,43 +2526,6 @@
     }
 
 
-    /**
-     * Translate UID to message ID
-     *
-     * @param int    $uid     Message UID
-     * @param string $mailbox Mailbox name
-     *
-     * @return int   Message ID
-     */
-    function get_id($uid, $mailbox=null)
-    {
-        if (!strlen($mailbox)) {
-            $mailbox = $this->mailbox;
-        }
-
-        return $this->_uid2id($uid, $mailbox);
-    }
-
-
-    /**
-     * Translate message number to UID
-     *
-     * @param int    $id      Message ID
-     * @param string $mailbox Mailbox name
-     *
-     * @return int   Message UID
-     */
-    function get_uid($id, $mailbox=null)
-    {
-        if (!strlen($mailbox)) {
-            $mailbox = $this->mailbox;
-        }
-
-        return $this->_id2uid($id, $mailbox);
-    }
-
-
-
     /* --------------------------------
      *        folder managment
      * --------------------------------*/
@@ -3017,47 +2533,22 @@
     /**
      * Public method for listing subscribed folders
      *
-     * @param   string  $root   Optional root folder
-     * @param   string  $name   Optional name pattern
-     * @param   string  $filter Optional filter
+     * @param   string  $root      Optional root folder
+     * @param   string  $name      Optional name pattern
+     * @param   string  $filter    Optional filter
+     * @param   string  $rights    Optional ACL requirements
+     * @param   bool    $skip_sort Enable to return unsorted list (for better performance)
      *
-     * @return  array   List of mailboxes/folders
+     * @return  array   List of folders
      * @access  public
      */
-    function list_mailboxes($root='', $name='*', $filter=null)
-    {
-        $a_mboxes = $this->_list_mailboxes($root, $name, $filter);
-
-        // INBOX should always be available
-        if ((!$filter || $filter == 'mail') && !in_array('INBOX', $a_mboxes)) {
-            array_unshift($a_mboxes, 'INBOX');
-        }
-
-        // sort mailboxes
-        $a_mboxes = $this->_sort_mailbox_list($a_mboxes);
-
-        return $a_mboxes;
-    }
-
-
-    /**
-     * Private method for mailbox listing
-     *
-     * @param   string  $root   Optional root folder
-     * @param   string  $name   Optional name pattern
-     * @param   mixed   $filter Optional filter
-     *
-     * @return  array   List of mailboxes/folders
-     * @see     rcube_imap::list_mailboxes()
-     * @access  private
-     */
-    private function _list_mailboxes($root='', $name='*', $filter=null)
+    function list_mailboxes($root='', $name='*', $filter=null, $rights=null, $skip_sort=false)
     {
         $cache_key = $root.':'.$name;
         if (!empty($filter)) {
             $cache_key .= ':'.(is_string($filter) ? $filter : serialize($filter));
         }
-
+        $cache_key .= ':'.$rights;
         $cache_key = 'mailboxes.'.md5($cache_key);
 
         // get cached folder list
@@ -3066,6 +2557,48 @@
             return $a_mboxes;
         }
 
+        $a_mboxes = $this->_list_mailboxes($root, $name, $filter, $rights);
+
+        if (!is_array($a_mboxes)) {
+            return array();
+        }
+
+        // filter folders list according to rights requirements
+        if ($rights && $this->get_capability('ACL')) {
+            $a_mboxes = $this->filter_rights($a_mboxes, $rights);
+        }
+
+        // INBOX should always be available
+        if ((!$filter || $filter == 'mail') && !in_array('INBOX', $a_mboxes)) {
+            array_unshift($a_mboxes, 'INBOX');
+        }
+
+        // sort mailboxes (always sort for cache)
+        if (!$skip_sort || $this->cache) {
+            $a_mboxes = $this->_sort_mailbox_list($a_mboxes);
+        }
+
+        // write mailboxlist to cache
+        $this->update_cache($cache_key, $a_mboxes);
+
+        return $a_mboxes;
+    }
+
+
+    /**
+     * Private method for mailbox listing (LSUB)
+     *
+     * @param   string  $root   Optional root folder
+     * @param   string  $name   Optional name pattern
+     * @param   mixed   $filter Optional filter
+     * @param   string  $rights Optional ACL requirements
+     *
+     * @return  array   List of subscribed folders
+     * @see     rcube_imap::list_mailboxes()
+     * @access  private
+     */
+    private function _list_mailboxes($root='', $name='*', $filter=null, $rights=null)
+    {
         $a_defaults = $a_out = array();
 
         // Give plugins a chance to provide a list of mailboxes
@@ -3074,6 +2607,9 @@
 
         if (isset($data['folders'])) {
             $a_folders = $data['folders'];
+        }
+        else if (!$this->conn->connected()) {
+           return null;
         }
         else {
             // Server supports LIST-EXTENDED, we can use selection options
@@ -3084,29 +2620,42 @@
                 $a_folders = $this->conn->listMailboxes($root, $name,
                     NULL, array('SUBSCRIBED'));
 
-                // remove non-existent folders
-                if (is_array($a_folders)) {
+                // unsubscribe non-existent folders, remove from the list
+                if (is_array($a_folders) && $name == '*') {
                     foreach ($a_folders as $idx => $folder) {
                         if ($this->conn->data['LIST'] && ($opts = $this->conn->data['LIST'][$folder])
                             && in_array('\\NonExistent', $opts)
                         ) {
+                            $this->conn->unsubscribe($folder);
                             unset($a_folders[$idx]);
-                        } 
+                        }
                     }
                 }
             }
             // retrieve list of folders from IMAP server using LSUB
             else {
                 $a_folders = $this->conn->listSubscribed($root, $name);
+
+                // unsubscribe non-existent folders, remove from the list
+                if (is_array($a_folders) && $name == '*') {
+                    foreach ($a_folders as $idx => $folder) {
+                        if ($this->conn->data['LIST'] && ($opts = $this->conn->data['LIST'][$folder])
+                            && in_array('\\Noselect', $opts)
+                        ) {
+                            // Some servers returns \Noselect for existing folders
+                            if (!$this->mailbox_exists($folder)) {
+                                $this->conn->unsubscribe($folder);
+                                unset($a_folders[$idx]);
+                            }
+                        }
+                    }
+                }
             }
         }
 
         if (!is_array($a_folders) || !sizeof($a_folders)) {
             $a_folders = array();
         }
-
-        // write mailboxlist to cache
-        $this->update_cache($cache_key, $a_folders);
 
         return $a_folders;
     }
@@ -3115,15 +2664,29 @@
     /**
      * Get a list of all folders available on the IMAP server
      *
-     * @param string $root   IMAP root dir
-     * @param string  $name   Optional name pattern
-     * @param mixed   $filter Optional filter
+     * @param string  $root      IMAP root dir
+     * @param string  $name      Optional name pattern
+     * @param mixed   $filter    Optional filter
+     * @param string  $rights    Optional ACL requirements
+     * @param bool    $skip_sort Enable to return unsorted list (for better performance)
      *
      * @return array Indexed array with folder names
      */
-    function list_unsubscribed($root='', $name='*', $filter=null)
+    function list_unsubscribed($root='', $name='*', $filter=null, $rights=null, $skip_sort=false)
     {
-        // @TODO: caching
+        $cache_key = $root.':'.$name;
+        if (!empty($filter)) {
+            $cache_key .= ':'.(is_string($filter) ? $filter : serialize($filter));
+        }
+        $cache_key .= ':'.$rights;
+        $cache_key = 'mailboxes.list.'.md5($cache_key);
+
+        // get cached folder list
+        $a_mboxes = $this->get_cache($cache_key);
+        if (is_array($a_mboxes)) {
+            return $a_mboxes;
+        }
+
         // Give plugins a chance to provide a list of mailboxes
         $data = rcmail::get_instance()->plugins->exec_hook('mailboxes_list',
             array('root' => $root, 'name' => $name, 'filter' => $filter, 'mode' => 'LIST'));
@@ -3133,7 +2696,7 @@
         }
         else {
             // retrieve list of folders from IMAP server
-            $a_mboxes = $this->conn->listMailboxes($root, $name);
+            $a_mboxes = $this->_list_unsubscribed($root, $name);
         }
 
         if (!is_array($a_mboxes)) {
@@ -3145,10 +2708,105 @@
             array_unshift($a_mboxes, 'INBOX');
         }
 
+        // cache folder attributes
+        if ($root == '' && $name == '*' && empty($filter)) {
+            $this->update_cache('mailboxes.attributes', $this->conn->data['LIST']);
+        }
+
+        // filter folders list according to rights requirements
+        if ($rights && $this->get_capability('ACL')) {
+            $a_folders = $this->filter_rights($a_folders, $rights);
+        }
+
         // filter folders and sort them
-        $a_mboxes = $this->_sort_mailbox_list($a_mboxes);
+        if (!$skip_sort) {
+            $a_mboxes = $this->_sort_mailbox_list($a_mboxes);
+        }
+
+        // write mailboxlist to cache
+        $this->update_cache($cache_key, $a_mboxes);
 
         return $a_mboxes;
+    }
+
+
+    /**
+     * Private method for mailbox listing (LIST)
+     *
+     * @param   string  $root   Optional root folder
+     * @param   string  $name   Optional name pattern
+     *
+     * @return  array   List of folders
+     * @see     rcube_imap::list_unsubscribed()
+     */
+    private function _list_unsubscribed($root='', $name='*')
+    {
+        $result = $this->conn->listMailboxes($root, $name);
+
+        if (!is_array($result)) {
+            return array();
+        }
+
+        // #1486796: some server configurations doesn't
+        // return folders in all namespaces, we'll try to detect that situation
+        // and ask for these namespaces separately
+        if ($root == '' && $name == '*') {
+            $delim     = $this->get_hierarchy_delimiter();
+            $namespace = $this->get_namespace();
+            $search    = array();
+
+            // build list of namespace prefixes
+            foreach ((array)$namespace as $ns) {
+                if (is_array($ns)) {
+                    foreach ($ns as $ns_data) {
+                        if (strlen($ns_data[0])) {
+                            $search[] = $ns_data[0];
+                        }
+                    }
+                }
+            }
+
+            if (!empty($search)) {
+                // go through all folders detecting namespace usage
+                foreach ($result as $folder) {
+                    foreach ($search as $idx => $prefix) {
+                        if (strpos($folder, $prefix) === 0) {
+                            unset($search[$idx]);
+                        }
+                    }
+                    if (empty($search)) {
+                        break;
+                    }
+                }
+
+                // get folders in hidden namespaces and add to the result
+                foreach ($search as $prefix) {
+                    $list = $this->conn->listMailboxes($prefix, $name);
+
+                    if (!empty($list)) {
+                        $result = array_merge($result, $list);
+                    }
+                }
+            }
+        }
+
+        return $result;
+    }
+
+
+    /**
+     * Filter the given list of folders according to access rights
+     */
+    private function filter_rights($a_folders, $rights)
+    {
+        $regex = '/('.$rights.')/';
+        foreach ($a_folders as $idx => $folder) {
+            $myrights = join('', (array)$this->my_rights($folder));
+            if ($myrights !== null && !preg_match($regex, $myrights))
+                unset($a_folders[$idx]);
+        }
+
+        return $a_folders;
     }
 
 
@@ -3280,15 +2938,18 @@
 
             // check if mailbox children are subscribed
             foreach ($a_subscribed as $c_subscribed) {
-                if (preg_match('/^'.preg_quote($mailbox.$delm, '/').'/', $c_subscribed)) {
+                if (strpos($c_subscribed, $mailbox.$delm) === 0) {
                     $this->conn->unsubscribe($c_subscribed);
                     $this->conn->subscribe(preg_replace('/^'.preg_quote($mailbox, '/').'/',
                         $new_name, $c_subscribed));
+
+                    // clear cache
+                    $this->clear_message_cache($c_subscribed);
                 }
             }
 
             // clear cache
-            $this->clear_message_cache($mailbox.'.msg');
+            $this->clear_message_cache($mailbox);
             $this->clear_cache('mailboxes', true);
         }
 
@@ -3321,16 +2982,16 @@
             $this->conn->unsubscribe($mailbox);
 
             foreach ($sub_mboxes as $c_mbox) {
-                if (preg_match('/^'.preg_quote($mailbox.$delm, '/').'/', $c_mbox)) {
+                if (strpos($c_mbox, $mailbox.$delm) === 0) {
                     $this->conn->unsubscribe($c_mbox);
                     if ($this->conn->deleteFolder($c_mbox)) {
-	                    $this->clear_message_cache($c_mbox.'.msg');
+	                    $this->clear_message_cache($c_mbox);
                     }
                 }
             }
 
             // clear mailbox-related cache
-            $this->clear_message_cache($mailbox.'.msg');
+            $this->clear_message_cache($mailbox);
             $this->clear_cache('mailboxes', true);
         }
 
@@ -3405,8 +3066,8 @@
         foreach ($this->namespace as $type => $namespace) {
             if (is_array($namespace)) {
                 foreach ($namespace as $ns) {
-                    if (strlen($ns[0])) {
-                        if ((strlen($ns[0])>1 && $mailbox == substr($ns[0], 0, -1))
+                    if ($len = strlen($ns[0])) {
+                        if (($len > 1 && $mailbox == substr($ns[0], 0, -1))
                             || strpos($mailbox, $ns[0]) === 0
                         ) {
                             return $type;
@@ -3460,32 +3121,64 @@
 
 
     /**
-     * Gets folder options from LIST response, e.g. \Noselect, \Noinferiors
+     * Gets folder attributes from LIST response, e.g. \Noselect, \Noinferiors
      *
      * @param string $mailbox Folder name
-     * @param bool   $force   Set to True if options should be refreshed
-     *                        Options are available after LIST command only
+     * @param bool   $force   Set to True if attributes should be refreshed
      *
      * @return array Options list
      */
-    function mailbox_options($mailbox, $force=false)
+    function mailbox_attributes($mailbox, $force=false)
     {
-        if ($mailbox == 'INBOX') {
-            return array();
+        // get attributes directly from LIST command
+        if (!empty($this->conn->data['LIST']) && is_array($this->conn->data['LIST'][$mailbox])) {
+            $opts = $this->conn->data['LIST'][$mailbox];
+        }
+        // get cached folder attributes
+        else if (!$force) {
+            $opts = $this->get_cache('mailboxes.attributes');
+            $opts = $opts[$mailbox];
         }
 
-        if (!is_array($this->conn->data['LIST']) || !is_array($this->conn->data['LIST'][$mailbox])) {
-            if ($force) {
-                $this->conn->listMailboxes('', $mailbox);
-            }
-            else {
-                return array();
-            }
+        if (!is_array($opts)) {
+            $this->conn->listMailboxes('', $mailbox);
+            $opts = $this->conn->data['LIST'][$mailbox];
         }
-
-        $opts = $this->conn->data['LIST'][$mailbox];
 
         return is_array($opts) ? $opts : array();
+    }
+
+
+    /**
+     * Gets connection (and current mailbox) data: UIDVALIDITY, EXISTS, RECENT,
+     * PERMANENTFLAGS, UIDNEXT, UNSEEN
+     *
+     * @param string $mailbox Folder name
+     *
+     * @return array Data
+     */
+    function mailbox_data($mailbox)
+    {
+        if (!strlen($mailbox))
+            $mailbox = $this->mailbox !== null ? $this->mailbox : 'INBOX';
+
+        if ($this->conn->selected != $mailbox) {
+            if ($this->conn->select($mailbox))
+                $this->mailbox = $mailbox;
+            else
+                return null;
+        }
+
+        $data = $this->conn->data;
+
+        // add (E)SEARCH result for ALL UNDELETED query
+        if (!empty($this->icache['undeleted_idx'])
+            && $this->icache['undeleted_idx']->getParameters('MAILBOX') == $mailbox
+        ) {
+            $data['UNDELETED'] = $this->icache['undeleted_idx'];
+        }
+
+        return $data;
     }
 
 
@@ -3498,6 +3191,10 @@
      */
     function mailbox_info($mailbox)
     {
+        if ($this->icache['options'] && $this->icache['options']['name'] == $mailbox) {
+            return $this->icache['options'];
+        }
+
         $acl       = $this->get_capability('ACL');
         $namespace = $this->get_namespace();
         $options   = array();
@@ -3510,23 +3207,37 @@
                     foreach ($ns as $item) {
                         if ($item[0] === $mbox) {
                             $options['is_root'] = true;
-                            break;
+                            break 2;
                         }
                     }
                 }
             }
         }
+        // check if the folder is other user virtual-root
+        if (!$options['is_root'] && !empty($namespace) && !empty($namespace['other'])) {
+            $parts = explode($this->delimiter, $mailbox);
+            if (count($parts) == 2) {
+                $mbox = $parts[0] . $this->delimiter;
+                foreach ($namespace['other'] as $item) {
+                    if ($item[0] === $mbox) {
+                        $options['is_root'] = true;
+                        break;
+                    }
+                }
+            }
+        }
 
-        $options['name']      = $mailbox;
-        $options['options']   = $this->mailbox_options($mailbox, true);
-        $options['namespace'] = $this->mailbox_namespace($mailbox);
-        $options['rights']    = $acl && !$options['is_root'] ? (array)$this->my_rights($mailbox) : array();
-        $options['special']   = in_array($mailbox, $this->default_folders);
+        $options['name']       = $mailbox;
+        $options['attributes'] = $this->mailbox_attributes($mailbox, true);
+        $options['namespace']  = $this->mailbox_namespace($mailbox);
+        $options['rights']     = $acl && !$options['is_root'] ? (array)$this->my_rights($mailbox) : array();
+        $options['special']    = in_array($mailbox, $this->default_folders);
 
-        if (is_array($options['options'])) {
-            foreach ($options['options'] as $opt) {
-                $opt = strtolower($opt);
-                if ($opt == '\noselect' || $opt == '\nonexistent') {
+        // Set 'noselect' and 'norename' flags
+        if (is_array($options['attributes'])) {
+            foreach ($options['attributes'] as $attrib) {
+                $attrib = strtolower($attrib);
+                if ($attrib == '\noselect' || $attrib == '\nonexistent') {
                     $options['noselect'] = true;
                 }
             }
@@ -3536,14 +3247,32 @@
         }
 
         if (!empty($options['rights'])) {
-            $options['norename'] = !in_array('x', $options['rights']) &&
-                (!in_array('c', $options['rights']) || !in_array('d', $options['rights']));
+            $options['norename'] = !in_array('x', $options['rights']) && !in_array('d', $options['rights']);
+
             if (!$options['noselect']) {
                 $options['noselect'] = !in_array('r', $options['rights']);
             }
         }
+        else {
+            $options['norename'] = $options['is_root'] || $options['namespace'] != 'personal';
+        }
+
+        $this->icache['options'] = $options;
 
         return $options;
+    }
+
+
+    /**
+     * Synchronizes messages cache.
+     *
+     * @param string $mailbox Folder name
+     */
+    public function mailbox_sync($mailbox)
+    {
+        if ($mcache = $this->get_mcache_engine()) {
+            $mcache->synchronize($mailbox);
+        }
     }
 
 
@@ -3759,7 +3488,7 @@
             // @TODO: Honor MAXSIZE and DEPTH options
             foreach ($queries as $attrib => $entry)
                 if ($result = $this->conn->getAnnotation($mailbox, $entry, $attrib))
-                    $res = array_merge($res, $result);
+                    $res = array_merge_recursive($res, $result);
 
             return $res;
         }
@@ -3797,22 +3526,34 @@
     /**
      * Enable or disable indexes caching
      *
-     * @param boolean $type Cache type (@see rcmail::get_cache)
+     * @param string $type Cache type (@see rcmail::get_cache)
      * @access public
      */
     function set_caching($type)
     {
         if ($type) {
-            $rcmail = rcmail::get_instance();
-            $this->cache = $rcmail->get_cache('IMAP', $type);
+            $this->caching = $type;
         }
         else {
             if ($this->cache)
                 $this->cache->close();
-            $this->cache = null;
+            $this->cache   = null;
+            $this->caching = false;
         }
     }
 
+    /**
+     * Getter for IMAP cache object
+     */
+    private function get_cache_engine()
+    {
+        if ($this->caching && !$this->cache) {
+            $rcmail = rcmail::get_instance();
+            $this->cache = $rcmail->get_cache('IMAP', $this->caching);
+        }
+
+        return $this->cache;
+    }
 
     /**
      * Returns cached value
@@ -3823,8 +3564,8 @@
      */
     function get_cache($key)
     {
-        if ($this->cache) {
-            return $this->cache->get($key);
+        if ($cache = $this->get_cache_engine()) {
+            return $cache->get($key);
         }
     }
 
@@ -3837,8 +3578,8 @@
      */
     function update_cache($key, $data)
     {
-        if ($this->cache) {
-            $this->cache->set($key, $data);
+        if ($cache = $this->get_cache_engine()) {
+            $cache->set($key, $data);
         }
     }
 
@@ -3852,8 +3593,8 @@
      */
     function clear_cache($key=null, $prefix_mode=false)
     {
-        if ($this->cache) {
-            $this->cache->remove($key, $prefix_mode);
+        if ($cache = $this->get_cache_engine()) {
+            $cache->remove($key, $prefix_mode);
         }
     }
 
@@ -3866,418 +3607,49 @@
      * Enable or disable messages caching
      *
      * @param boolean $set Flag
-     * @access public
      */
     function set_messages_caching($set)
     {
-        $rcmail = rcmail::get_instance();
-
-        if ($set && ($dbh = $rcmail->get_dbh())) {
-            $this->db = $dbh;
+        if ($set) {
             $this->messages_caching = true;
         }
         else {
+            if ($this->mcache)
+                $this->mcache->close();
+            $this->mcache = null;
             $this->messages_caching = false;
         }
     }
 
     /**
-     * Checks if the cache is up-to-date
+     * Getter for messages cache object
+     */
+    private function get_mcache_engine()
+    {
+        if ($this->messages_caching && !$this->mcache) {
+            $rcmail = rcmail::get_instance();
+            if ($dbh = $rcmail->get_dbh()) {
+                $this->mcache = new rcube_imap_cache(
+                    $dbh, $this, $rcmail->user->ID, $this->skip_deleted);
+            }
+        }
+
+        return $this->mcache;
+    }
+
+    /**
+     * Clears the messages cache.
      *
-     * @param string $mailbox   Mailbox name
-     * @param string $cache_key Internal cache key
-     * @return int   Cache status: -3 = off, -2 = incomplete, -1 = dirty, 1 = OK
+     * @param string $mailbox Folder name
+     * @param array  $uids    Optional message UIDs to remove from cache
      */
-    private function check_cache_status($mailbox, $cache_key)
+    function clear_message_cache($mailbox = null, $uids = null)
     {
-        if (!$this->messages_caching)
-            return -3;
-
-        $cache_index = $this->get_message_cache_index($cache_key);
-        $msg_count = $this->_messagecount($mailbox);
-        $cache_count = count($cache_index);
-
-        // empty mailbox
-        if (!$msg_count) {
-            return $cache_count ? -2 : 1;
+        if ($mcache = $this->get_mcache_engine()) {
+            $mcache->clear($mailbox, $uids);
         }
-
-        if ($cache_count == $msg_count) {
-            if ($this->skip_deleted) {
-                if (!empty($this->icache['all_undeleted_idx'])) {
-                    $uids = rcube_imap_generic::uncompressMessageSet($this->icache['all_undeleted_idx']);
-                    $uids = array_flip($uids);
-                    foreach ($cache_index as $uid) {
-                        unset($uids[$uid]);
-                    }
-                }
-                else {
-                    // get all undeleted messages excluding cached UIDs
-                    $uids = $this->search_once($mailbox, 'ALL UNDELETED NOT UID '.
-                        rcube_imap_generic::compressMessageSet($cache_index));
-                }
-                if (empty($uids)) {
-                    return 1;
-                }
-            } else {
-                // get UID of the message with highest index
-                $uid = $this->_id2uid($msg_count, $mailbox);
-                $cache_uid = array_pop($cache_index);
-
-                // uids of highest message matches -> cache seems OK
-                if ($cache_uid == $uid) {
-                    return 1;
-                }
-            }
-            // cache is dirty
-            return -1;
-        }
-
-        // if cache count differs less than 10% report as dirty
-        return (abs($msg_count - $cache_count) < $msg_count/10) ? -1 : -2;
     }
 
-
-    /**
-     * @param string $key Cache key
-     * @param string $from
-     * @param string $to
-     * @param string $sort_field
-     * @param string $sort_order
-     * @access private
-     */
-    private function get_message_cache($key, $from, $to, $sort_field, $sort_order)
-    {
-        if (!$this->messages_caching)
-            return NULL;
-
-        // use idx sort as default sorting
-        if (!$sort_field || !in_array($sort_field, $this->db_header_fields)) {
-            $sort_field = 'idx';
-        }
-
-        $result = array();
-
-        $sql_result = $this->db->limitquery(
-                "SELECT idx, uid, headers".
-                " FROM ".get_table_name('messages').
-                " WHERE user_id=?".
-                " AND cache_key=?".
-                " ORDER BY ".$this->db->quoteIdentifier($sort_field)." ".strtoupper($sort_order),
-                $from,
-                $to - $from,
-                $_SESSION['user_id'],
-                $key);
-
-        while ($sql_arr = $this->db->fetch_assoc($sql_result)) {
-            $uid = intval($sql_arr['uid']);
-            $result[$uid] = $this->db->decode(unserialize($sql_arr['headers']));
-
-            // featch headers if unserialize failed
-            if (empty($result[$uid]))
-                $result[$uid] = $this->conn->fetchHeader(
-                    preg_replace('/.msg$/', '', $key), $uid, true, false, $this->get_fetch_headers());
-        }
-
-        return $result;
-    }
-
-
-    /**
-     * @param string $key Cache key
-     * @param int    $uid Message UID
-     * @return mixed
-     * @access private
-     */
-    private function &get_cached_message($key, $uid)
-    {
-        $internal_key = 'message';
-
-        if ($this->messages_caching && !isset($this->icache[$internal_key][$uid])) {
-            $sql_result = $this->db->query(
-                "SELECT idx, headers, structure, message_id".
-                " FROM ".get_table_name('messages').
-                " WHERE user_id=?".
-                " AND cache_key=?".
-                " AND uid=?",
-                $_SESSION['user_id'],
-                $key,
-                $uid);
-
-            if ($sql_arr = $this->db->fetch_assoc($sql_result)) {
-                $this->icache['message.id'][$uid] = intval($sql_arr['message_id']);
-	            $this->uid_id_map[preg_replace('/\.msg$/', '', $key)][$uid] = intval($sql_arr['idx']);
-                $this->icache[$internal_key][$uid] = $this->db->decode(unserialize($sql_arr['headers']));
-
-                if (is_object($this->icache[$internal_key][$uid]) && !empty($sql_arr['structure']))
-                    $this->icache[$internal_key][$uid]->structure = $this->db->decode(unserialize($sql_arr['structure']));
-            }
-        }
-
-        return $this->icache[$internal_key][$uid];
-    }
-
-
-    /**
-     * @param string  $key        Cache key
-     * @param string  $sort_field Sorting column
-     * @param string  $sort_order Sorting order
-     * @return array Messages index
-     * @access private
-     */
-    private function get_message_cache_index($key, $sort_field='idx', $sort_order='ASC')
-    {
-        if (!$this->messages_caching || empty($key))
-            return NULL;
-
-        // use idx sort as default
-        if (!$sort_field || !in_array($sort_field, $this->db_header_fields))
-            $sort_field = 'idx';
-
-        if (array_key_exists('index', $this->icache)
-            && $this->icache['index']['key'] == $key
-            && $this->icache['index']['sort_field'] == $sort_field
-        ) {
-            if ($this->icache['index']['sort_order'] == $sort_order)
-                return $this->icache['index']['result'];
-            else
-                return array_reverse($this->icache['index']['result'], true);
-        }
-
-        $this->icache['index'] = array(
-            'result'     => array(),
-            'key'        => $key,
-            'sort_field' => $sort_field,
-            'sort_order' => $sort_order,
-        );
-
-        $sql_result = $this->db->query(
-            "SELECT idx, uid".
-            " FROM ".get_table_name('messages').
-            " WHERE user_id=?".
-            " AND cache_key=?".
-            " ORDER BY ".$this->db->quote_identifier($sort_field)." ".$sort_order,
-            $_SESSION['user_id'],
-            $key);
-
-        while ($sql_arr = $this->db->fetch_assoc($sql_result))
-            $this->icache['index']['result'][$sql_arr['idx']] = intval($sql_arr['uid']);
-
-        return $this->icache['index']['result'];
-    }
-
-
-    /**
-     * @access private
-     */
-    private function add_message_cache($key, $index, $headers, $struct=null, $force=false, $internal_cache=false)
-    {
-        if (empty($key) || !is_object($headers) || empty($headers->uid))
-            return;
-
-        // add to internal (fast) cache
-        if ($internal_cache) {
-            $this->icache['message'][$headers->uid] = clone $headers;
-            $this->icache['message'][$headers->uid]->structure = $struct;
-        }
-
-        // no further caching
-        if (!$this->messages_caching)
-            return;
-
-        // known message id
-        if (is_int($force) && $force > 0) {
-            $message_id = $force;
-        }
-        // check for an existing record (probably headers are cached but structure not)
-        else if (!$force) {
-            $sql_result = $this->db->query(
-                "SELECT message_id".
-                " FROM ".get_table_name('messages').
-                " WHERE user_id=?".
-                " AND cache_key=?".
-                " AND uid=?",
-                $_SESSION['user_id'],
-                $key,
-                $headers->uid);
-
-            if ($sql_arr = $this->db->fetch_assoc($sql_result))
-                $message_id = $sql_arr['message_id'];
-        }
-
-        // update cache record
-        if ($message_id) {
-            $this->db->query(
-                "UPDATE ".get_table_name('messages').
-                " SET idx=?, headers=?, structure=?".
-                " WHERE message_id=?",
-                $index,
-                serialize($this->db->encode(clone $headers)),
-                is_object($struct) ? serialize($this->db->encode(clone $struct)) : NULL,
-                $message_id
-            );
-        }
-        else { // insert new record
-            $this->db->query(
-                "INSERT INTO ".get_table_name('messages').
-                " (user_id, del, cache_key, created, idx, uid, subject, ".
-                $this->db->quoteIdentifier('from').", ".
-                $this->db->quoteIdentifier('to').", ".
-                "cc, date, size, headers, structure)".
-                " VALUES (?, 0, ?, ".$this->db->now().", ?, ?, ?, ?, ?, ?, ".
-                $this->db->fromunixtime($headers->timestamp).", ?, ?, ?)",
-                $_SESSION['user_id'],
-                $key,
-                $index,
-                $headers->uid,
-                (string)mb_substr($this->db->encode($this->decode_header($headers->subject, true)), 0, 128),
-                (string)mb_substr($this->db->encode($this->decode_header($headers->from, true)), 0, 128),
-                (string)mb_substr($this->db->encode($this->decode_header($headers->to, true)), 0, 128),
-                (string)mb_substr($this->db->encode($this->decode_header($headers->cc, true)), 0, 128),
-                (int)$headers->size,
-                serialize($this->db->encode(clone $headers)),
-                is_object($struct) ? serialize($this->db->encode(clone $struct)) : NULL
-            );
-        }
-
-        unset($this->icache['index']);
-    }
-
-
-    /**
-     * @access private
-     */
-    private function remove_message_cache($key, $ids, $idx=false)
-    {
-        if (!$this->messages_caching)
-            return;
-
-        $this->db->query(
-            "DELETE FROM ".get_table_name('messages').
-            " WHERE user_id=?".
-            " AND cache_key=?".
-            " AND ".($idx ? "idx" : "uid")." IN (".$this->db->array2list($ids, 'integer').")",
-            $_SESSION['user_id'],
-            $key);
-
-        unset($this->icache['index']);
-    }
-
-
-    /**
-     * @param string $key         Cache key
-     * @param int    $start_index Start index
-     * @access private
-     */
-    private function clear_message_cache($key, $start_index=1)
-    {
-        if (!$this->messages_caching)
-            return;
-
-        $this->db->query(
-            "DELETE FROM ".get_table_name('messages').
-            " WHERE user_id=?".
-            " AND cache_key=?".
-            " AND idx>=?",
-            $_SESSION['user_id'], $key, $start_index);
-
-        unset($this->icache['index']);
-    }
-
-
-    /**
-     * @access private
-     */
-    private function get_message_cache_index_min($key, $uids=NULL)
-    {
-        if (!$this->messages_caching)
-            return;
-
-        if (!empty($uids) && !is_array($uids)) {
-            if ($uids == '*' || $uids == '1:*')
-                $uids = NULL;
-            else
-                $uids = explode(',', $uids);
-        }
-
-        $sql_result = $this->db->query(
-            "SELECT MIN(idx) AS minidx".
-            " FROM ".get_table_name('messages').
-            " WHERE  user_id=?".
-            " AND    cache_key=?"
-            .(!empty($uids) ? " AND uid IN (".$this->db->array2list($uids, 'integer').")" : ''),
-            $_SESSION['user_id'],
-            $key);
-
-        if ($sql_arr = $this->db->fetch_assoc($sql_result))
-            return $sql_arr['minidx'];
-        else
-            return 0;
-    }
-
-
-    /**
-     * @param string $key Cache key
-     * @param int    $id  Message (sequence) ID
-     * @return int Message UID
-     * @access private
-     */
-    private function get_cache_id2uid($key, $id)
-    {
-        if (!$this->messages_caching)
-            return null;
-
-        if (array_key_exists('index', $this->icache)
-            && $this->icache['index']['key'] == $key
-        ) {
-            return $this->icache['index']['result'][$id];
-        }
-
-        $sql_result = $this->db->query(
-            "SELECT uid".
-            " FROM ".get_table_name('messages').
-            " WHERE user_id=?".
-            " AND cache_key=?".
-            " AND idx=?",
-            $_SESSION['user_id'], $key, $id);
-
-        if ($sql_arr = $this->db->fetch_assoc($sql_result))
-            return intval($sql_arr['uid']);
-
-        return null;
-    }
-
-
-    /**
-     * @param string $key Cache key
-     * @param int    $uid Message UID
-     * @return int Message (sequence) ID
-     * @access private
-     */
-    private function get_cache_uid2id($key, $uid)
-    {
-        if (!$this->messages_caching)
-            return null;
-
-        if (array_key_exists('index', $this->icache)
-            && $this->icache['index']['key'] == $key
-        ) {
-            return array_search($uid, $this->icache['index']['result']);
-        }
-
-        $sql_result = $this->db->query(
-            "SELECT idx".
-            " FROM ".get_table_name('messages').
-            " WHERE user_id=?".
-            " AND cache_key=?".
-            " AND uid=?",
-            $_SESSION['user_id'], $key, $uid);
-
-        if ($sql_arr = $this->db->fetch_assoc($sql_result))
-            return intval($sql_arr['idx']);
-
-        return null;
-    }
 
 
     /* --------------------------------
@@ -4373,7 +3745,7 @@
         $input = preg_replace("/\?=\s+=\?/", '?==?', $input);
 
         // encoded-word regexp
-        $re = '/=\?([^?]+)\?([BbQq])\?([^?\n]*)\?=/';
+        $re = '/=\?([^?]+)\?([BbQq])\?([^\n]*?)\?=/';
 
         // Find all RFC2047's encoded words
         if (preg_match_all($re, $input, $matches, PREG_OFFSET_CAPTURE | PREG_SET_ORDER)) {
@@ -4477,23 +3849,6 @@
     }
 
 
-    /**
-     * Convert body charset to RCMAIL_CHARSET according to the ctype_parameters
-     *
-     * @param string $body        Part body to decode
-     * @param string $ctype_param Charset to convert from
-     * @return string Content converted to internal charset
-     */
-    function charset_decode($body, $ctype_param)
-    {
-        if (is_array($ctype_param) && !empty($ctype_param['charset']))
-            return rcube_charset_convert($body, $ctype_param['charset']);
-
-        // defaults to what is specified in the class header
-        return rcube_charset_convert($body,  $this->default_charset);
-    }
-
-
     /* --------------------------------
      *         private methods
      * --------------------------------*/
@@ -4505,7 +3860,7 @@
      * @param string $sort_order Sort order
      * @access private
      */
-    private function _set_sort_order($sort_field, $sort_order)
+    private function set_sort_order($sort_field, $sort_order)
     {
         if ($sort_field != null)
             $this->sort_field = asciiwords($sort_field);
@@ -4575,36 +3930,14 @@
 
 
     /**
-     * @param int    $uid     Message UID
-     * @param string $mailbox Mailbox name
-     * @return int Message (sequence) ID
-     * @access private
-     */
-    private function _uid2id($uid, $mailbox=NULL)
-    {
-        if (!strlen($mailbox)) {
-            $mailbox = $this->mailbox;
-        }
-
-        if (!isset($this->uid_id_map[$mailbox][$uid])) {
-            if (!($id = $this->get_cache_uid2id($mailbox.'.msg', $uid)))
-                $id = $this->conn->UID2ID($mailbox, $uid);
-
-            $this->uid_id_map[$mailbox][$uid] = $id;
-        }
-
-        return $this->uid_id_map[$mailbox][$uid];
-    }
-
-
-    /**
-     * @param int    $id      Message (sequence) ID
-     * @param string $mailbox Mailbox name
+     * Find UID of the specified message sequence ID
+     *
+     * @param int    $id       Message (sequence) ID
+     * @param string $mailbox  Mailbox name
      *
      * @return int Message UID
-     * @access private
      */
-    private function _id2uid($id, $mailbox=null)
+    function id2uid($id, $mailbox = null)
     {
         if (!strlen($mailbox)) {
             $mailbox = $this->mailbox;
@@ -4614,9 +3947,7 @@
             return $uid;
         }
 
-        if (!($uid = $this->get_cache_id2uid($mailbox.'.msg', $id))) {
-            $uid = $this->conn->ID2UID($mailbox, $id);
-        }
+        $uid = $this->conn->ID2UID($mailbox, $id);
 
         $this->uid_id_map[$mailbox][$uid] = $id;
 
@@ -4733,16 +4064,19 @@
         $str = self::explode_header_string(',;', $str, true);
         $result = array();
 
+        // simplified regexp, supporting quoted local part
+        $email_rx = '(\S+|("\s*(?:[^"\f\n\r\t\v\b\s]+\s*)+"))@\S+';
+
         foreach ($str as $key => $val) {
             $name    = '';
             $address = '';
             $val     = trim($val);
 
-            if (preg_match('/(.*)<(\S+@\S+)>$/', $val, $m)) {
+            if (preg_match('/(.*)<('.$email_rx.')>$/', $val, $m)) {
                 $address = $m[2];
                 $name    = trim($m[1]);
             }
-            else if (preg_match('/^(\S+@\S+)$/', $val, $m)) {
+            else if (preg_match('/^('.$email_rx.')$/', $val, $m)) {
                 $address = $m[1];
                 $name    = '';
             }
@@ -4752,7 +4086,7 @@
 
             // dequote and/or decode name
             if ($name) {
-                if ($name[0] == '"') {
+                if ($name[0] == '"' && $name[strlen($name)-1] == '"') {
                     $name = substr($name, 1, -1);
                     $name = stripslashes($name);
                 }
@@ -4899,16 +4233,19 @@
  */
 class rcube_header_sorter
 {
-    var $sequence_numbers = array();
+    private $uids = array();
+
 
     /**
      * Set the predetermined sort order.
      *
-     * @param array $seqnums Numerically indexed array of IMAP message sequence numbers
+     * @param array $index  Numerically indexed array of IMAP UIDs
      */
-    function set_sequence_numbers($seqnums)
+    function set_index($index)
     {
-        $this->sequence_numbers = array_flip($seqnums);
+        $index = array_flip($index);
+
+        $this->uids = $index;
     }
 
     /**
@@ -4918,31 +4255,20 @@
      */
     function sort_headers(&$headers)
     {
-        /*
-        * uksort would work if the keys were the sequence number, but unfortunately
-        * the keys are the UIDs.  We'll use uasort instead and dereference the value
-        * to get the sequence number (in the "id" field).
-        *
-        * uksort($headers, array($this, "compare_seqnums"));
-        */
-        uasort($headers, array($this, "compare_seqnums"));
+        uksort($headers, array($this, "compare_uids"));
     }
 
     /**
-     * Sort method called by uasort()
+     * Sort method called by uksort()
      *
-     * @param rcube_mail_header $a
-     * @param rcube_mail_header $b
+     * @param int $a Array key (UID)
+     * @param int $b Array key (UID)
      */
-    function compare_seqnums($a, $b)
+    function compare_uids($a, $b)
     {
-        // First get the sequence number from the header object (the 'id' field).
-        $seqa = $a->id;
-        $seqb = $b->id;
-
         // then find each sequence number in my ordered list
-        $posa = isset($this->sequence_numbers[$seqa]) ? intval($this->sequence_numbers[$seqa]) : -1;
-        $posb = isset($this->sequence_numbers[$seqb]) ? intval($this->sequence_numbers[$seqb]) : -1;
+        $posa = isset($this->uids[$a]) ? intval($this->uids[$a]) : -1;
+        $posb = isset($this->uids[$b]) ? intval($this->uids[$b]) : -1;
 
         // return the relative position as the comparison value
         return $posa - $posb;

--
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