Applied message threading patch from Chris January: http://www.atomice.com/blog/?p=33

15 files changed, 922 insertions, 120 deletions

diff --git a/roundcubemail/program/include/rcmail.php b/roundcubemail/program/include/rcmail.php
index f109c16fd..96937b58a 100644
--- a/roundcubemail/program/include/rcmail.php
+++ b/roundcubemail/program/include/rcmail.php
@@ -349,6 +349,10 @@ class rcmail
     if ($this->config->get('enable_caching')) {
       $this->imap->set_caching(true);
     }
+    
+    if ($this->config->get('enable_thread_caching')) {
+      $this->imap->set_thread_caching(true);
+    }
 
     // set pagesize from config
     $this->imap->set_pagesize($this->config->get('pagesize', 50));
diff --git a/roundcubemail/program/include/rcube_imap.php b/roundcubemail/program/include/rcube_imap.php
index 637e25b92..788b0ff58 100644
--- a/roundcubemail/program/include/rcube_imap.php
+++ b/roundcubemail/program/include/rcube_imap.php
@@ -52,6 +52,7 @@ class rcube_imap
   var $sort_order = 'DESC';
   var $delimiter = NULL;
   var $caching_enabled = FALSE;
+  var $thread_caching_enabled = FALSE;
   var $default_charset = 'ISO-8859-1';
   var $default_folders = array('INBOX');
   var $default_folders_lc = array('inbox');
@@ -68,6 +69,7 @@ class rcube_imap
   var $debug_level = 1;
   var $error_code = 0;
   var $options = array('imap' => 'check');
+  var $threading = false;
 
 
   /**
@@ -472,7 +474,7 @@ class rcube_imap
       $mailbox = $this->mailbox;
       
     // count search set
-    if ($this->search_string && $mailbox == $this->mailbox && $mode == 'ALL' && !$force)
+    if ($this->search_string && $mailbox == $this->mailbox && ($mode == 'ALL' || $mode == 'THREADS') && !$force)
       return count((array)$this->search_set);
 
     $a_mailbox_cache = $this->get_cache('messagecount');
@@ -481,8 +483,12 @@ class rcube_imap
     if (!$force && is_array($a_mailbox_cache[$mailbox]) && isset($a_mailbox_cache[$mailbox][$mode]))
       return $a_mailbox_cache[$mailbox][$mode];
 
+    if ($this->get_capability('thread=references') &&
+        $mode == 'THREADS')
+      $count = $this->_threadcount($mailbox);
+
     // RECENT count is fetched a bit different
-    if ($mode == 'RECENT')
+    else if ($mode == 'RECENT')
        $count = iil_C_CheckForRecent($this->conn, $mailbox);
 
     // use SEARCH for message counting
@@ -524,6 +530,25 @@ class rcube_imap
     return (int)$count;
     }
 
+    function _threadcount($mailbox)
+    {
+        if (isset ($this->cache['__threads']['tree']))
+            return count($this->cache['__threads']['tree']);
+        if ($this->check_thread_cache_status($mailbox) > 0) {
+            $sql_result = $this->db->query("SELECT COUNT(*)
+                                            FROM " .
+                                           get_table_name('threads') . "
+                                            WHERE  user_id=? AND mailbox=?",
+                                           $_SESSION['user_id'],
+                                           $mailbox);
+
+            if ($sql_arr = $this->db->fetch_array($sql_result))
+                return $sql_arr[0];
+        }
+        list ($thread_tree, $msg_depth, $has_children) = iil_C_Thread($this->conn, $mailbox, 'REFERENCES', 'ALL');
+        $this->update_thread_cache($mailbox, $thread_tree, $msg_depth, $has_children);
+        return count($thread_tree);
+    }
 
   /**
    * Public method for listing headers
@@ -560,8 +585,9 @@ class rcube_imap
 
     $this->_set_sort_order($sort_field, $sort_order);
 
-    $max = $this->_messagecount($mailbox);
-    $start_msg = ($this->list_page-1) * $this->page_size;
+    $message_threading = $this->get_capability('thread=references') &&
+                         rcmail::get_instance()->imap->threading;
+    $max = $this->_messagecount($mailbox, $message_threading ? 'THREADS' : 'ALL');
 
     list($begin, $end) = $this->_get_message_range($max, $page);
 
@@ -573,65 +599,139 @@ class rcube_imap
     $cache_key = $mailbox.'.msg';
     $cache_status = $this->check_cache_status($mailbox, $cache_key);
 
-    // cache is OK, we can get all messages from local cache
-    if ($cache_status>0)
-      {
-      $a_msg_headers = $this->get_message_cache($cache_key, $start_msg, $start_msg+$this->page_size, $this->sort_field, $this->sort_order);
-      $headers_sorted = TRUE;
-      }
-    // cache is dirty, sync it
-    else if ($this->caching_enabled && $cache_status==-1 && !$recursive)
+    if ($cache_status <= 0 && $this->caching_enabled && $cache_status == -1 && !$recursive)
       {
       $this->sync_header_index($mailbox);
       return $this->_list_headers($mailbox, $page, $this->sort_field, $this->sort_order, TRUE);
       }
-    else
-      {
-      // retrieve headers from IMAP
-      if ($this->get_capability('sort') && ($msg_index = iil_C_Sort($this->conn, $mailbox, $this->sort_field, $this->skip_deleted ? 'UNDELETED' : '')))
-        {
-        $mymsgidx = array_slice ($msg_index, $begin, $end-$begin);
-        $msgs = join(",", $mymsgidx);
-        }
-      else
-        {
-        $msgs = sprintf("%d:%d", $begin+1, $end);
-        $msg_index = range($begin, $end);
-        }
 
+    if ($message_threading) {
+        $thread_cache_status = $this->check_thread_cache_status($mailbox);
+        if ($thread_cache_status > 0 && $cache_status > 0) {
+            // use a JOIN of the threads and messages tables to get a sorted list of roots
+            $roots = $this->get_thread_cache_roots_sorted($mailbox, $begin, $end, $this->sort_field, $this->sort_order);
+        } else {
+            if ($thread_cache_status > 0) {
+                // get a list of thread roots from the cache
+                $roots = $this->get_thread_cache_roots($mailbox);
+            } else {
+                if (isset ($this->cache['__threads']['tree'])) {
+                    $thread_tree = $this->cache['__threads']['tree'];
+                    $msg_depth = $this->cache['__threads']['depth'];
+                    $has_children = $this->cache['__threads']['has_children'];
+                } else {
+                    list ($thread_tree, $msg_depth, $has_children) = iil_C_Thread($this->conn, $mailbox, 'REFERENCES', 'ALL');
+                }
+                $this->update_thread_cache($mailbox, $thread_tree, $msg_depth, $has_children);
+                // the keys of thread_tree are the thread roots
+                $roots = array_keys($thread_tree);
+            }
+
+            if ($this->get_capability('sort') && ($sort_index = iil_C_Sort($this->conn, $mailbox, $this->sort_field, $this->skip_deleted ? 'UNDELETED' : ''))) {
+                if ($this->sort_order == 'DESC')
+                    $sort_index = array_reverse($sort_index);
+            } else {
+                if ($this->sort_order == 'DESC')
+                    $msg_index = range($max, 1);
+                else
+                    $msg_index = range(1, $max);
+            }
 
-      // fetch reuested headers from server
-      $a_msg_headers = array();
-      $deleted_count = $this->_fetch_headers($mailbox, $msgs, $a_msg_headers, $cache_key);
+            // sort the roots according to the order defined by $sort_index
+            $sorter = new rcube_thread_root_sorter();
+            $sorter->set_sequence_numbers($sort_index);
+            $sorter->sort_threads($roots);
+            
+            // get the roots for this page
+            $roots = array_slice($roots, $begin, $end - $begin);
+        }
 
-      // 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, $max + 1);
+        if ($thread_cache_status > 0) {
+        	// get the children of $roots from the cache
+            $threads = $this->get_thread_cache_threads($mailbox, $roots);
+            $msg_index = array ();
+            $msg_depth = array ();
+            $has_children = array ();
+            foreach ($threads as $thread) {
+                foreach ($thread as $msg) {
+                    $idx = $msg['idx'];
+                    $msg_index[] = $idx;
+                    $msg_depth[$idx] = $msg['depth'];
+                    $has_children[$idx] = $msg['has_children'];
+                }
+            }
+        } else {
+            // flatten the thread tree
+            $msg_index = array ();
+            foreach ($roots as $root) {
+                $msg_index[] = $root;
+                $msg_index = array_merge($msg_index, array_keys_recursive($thread_tree[$root]));
+            }
+        }
+    } else { // no threading
+        if ($this->get_capability('sort') && ($msg_index = iil_C_Sort($this->conn, $mailbox, $this->sort_field, $this->skip_deleted ? 'UNDELETED' : ''))) {
+            if ($this->sort_order == 'DESC')
+                 $msg_index = array_reverse($msg_index);
+            $msg_index = array_slice($msg_index, $begin, $end - $begin);
+        } else {
+            if ($this->sort_order == 'DESC')
+                $msg_index = range($end, $begin + 1);
+            else
+                $msg_index = range($begin + 1, $end);
+        }
+    }
 
-      // kick child process to sync cache
-      // ...
-      }
+    // fetch requested headers from server
+    $msgs = join(",", $msg_index);
+    // cache is OK, we can get all messages from local cache
+    if ($cache_status > 0) {
+        // if $message_threading is true then no point sorting them as they will need re-sorting later
+        $a_msg_headers = $this->get_message_cache($cache_key, $message_threading?null:$this->sort_field, $this->sort_order, $msgs);
+        // if $message_threading is true then $a_msg_headers will need re-sorting as the tree structure won't have been preserved'
+        $headers_sorted = !$message_threading;
+    } else {
+        $a_msg_headers = array();
+        $deleted_count = $this->_fetch_headers($mailbox, $msgs, $a_msg_headers, $cache_key);
+        // 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);
+    }
+
+    // kick child process to sync cache
+    // ...
 
     // return empty array if no messages found
     if (!is_array($a_msg_headers) || empty($a_msg_headers)) {
       return array();
     }
 
-    // if not already sorted
     if (!$headers_sorted)
       {
       // use this class for message sorting
       $sorter = new rcube_header_sorter();
       $sorter->set_sequence_numbers($msg_index);
       $sorter->sort_headers($a_msg_headers);
-
-      if ($this->sort_order == 'DESC')
-        $a_msg_headers = array_reverse($a_msg_headers);
       }
 
-    return array_values($a_msg_headers);
+    if ($message_threading) {
+       // Set depth, has_children and unread_children fields in headers 
+       $parents = array();
+       foreach ($a_msg_headers as $uid => $headers) {
+            $id = $headers->id;
+            $depth = $msg_depth[$id];
+            $parents = array_slice($parents, 0, $depth - 1);
+            if (!$headers->seen) {
+                foreach ($parents as $parent)
+                    $a_msg_headers[$parent]->unread_children++;
+            }
+            array_push($parents, $uid);
+            $a_msg_headers[$uid]->depth = $depth;
+            $a_msg_headers[$uid]->has_children = $has_children[$id];
+        }
     }
 
+    return array_values($a_msg_headers);
+    }
 
   /**
    * Private method for listing a set of message headers (search results)
@@ -738,11 +838,6 @@ class rcube_imap
       $begin = 0;
       $end = $max;
       }
-    else if ($this->sort_order=='DESC')
-      {
-      $begin = $max - $this->page_size - $start_msg;
-      $end =   $max - $start_msg;
-      }
     else
       {
       $begin = $start_msg;
@@ -756,8 +851,6 @@ class rcube_imap
     return array($begin, $end);
     }
     
-    
-
   /**
    * Fetches message headers
    * Used for loop
@@ -2046,6 +2139,17 @@ class rcube_imap
   /**
    * @access private
    */
+  function set_thread_caching($set)
+    {
+    if ($set && is_object($this->db))
+      $this->thread_caching_enabled = TRUE;
+    else
+      $this->thread_caching_enabled = FALSE;
+    }
+
+  /**
+   * @access private
+   */
   function get_cache($key)
     {
     // read cache
@@ -2226,6 +2330,9 @@ class rcube_imap
 
     if ($cache_count==$msg_count)
       {
+      if ($msg_count == 0)
+        return 1;
+
       // get highest index
       $header = iil_C_FetchHeader($this->conn, $mailbox, "$msg_count");
       $cache_uid = array_pop($cache_index);
@@ -2247,26 +2354,29 @@ class rcube_imap
   /**
    * @access private
    */
-  function get_message_cache($key, $from, $to, $sort_field, $sort_order)
+  function get_message_cache($key, $sort_field, $sort_order, $msgs)
     {
-    $cache_key = "$key:$from:$to:$sort_field:$sort_order";
+    $cache_key = "$key:$sort_field:$sort_order:$msgs";
     $db_header_fields = array('idx', 'uid', 'subject', 'from', 'to', 'cc', 'date', 'size');
     
-    if (!in_array($sort_field, $db_header_fields))
-      $sort_field = 'idx';
-    
     if ($this->caching_enabled && !isset($this->cache[$cache_key]))
       {
       $this->cache[$cache_key] = array();
-      $sql_result = $this->db->limitquery(
+      if (is_null($sort_field)) {
+          $sort = '';
+      } else {
+      	 if (!in_array($sort_field, $db_header_fields))
+              $sort_field = 'idx';
+          $sort = "ORDER BY ".$this->db->quoteIdentifier($sort_field)." ".
+                  strtoupper($sort_order);
+      }
+      $sql_result = $this->db->query(
         "SELECT idx, uid, headers
          FROM ".get_table_name('messages')."
          WHERE  user_id=?
          AND    cache_key=?
-         ORDER BY ".$this->db->quoteIdentifier($sort_field)." ".
-         strtoupper($sort_order),
-        $from,
-        $to-$from,
+         AND    idx IN ($msgs)
+         $sort",
         $_SESSION['user_id'],
         $key);
 
@@ -2444,8 +2554,175 @@ class rcube_imap
       $start_index);
     }
 
+    /* --------------------------------
+     *   thread caching methods
+     * --------------------------------*/
 
+    /**
+     * Checks if the thread cache is up-to-date
+     *
+     * @param string Mailbox name
+     * @return int 0 = ok, -1 = invalid, -2 = cache disabled
+     */
+    function check_thread_cache_status($mailbox)
+    {
+        if (!$this->caching_enabled)
+            return -2;
+
+        $cache_uid = $this->get_cache('thread_cache_last_uid');
+        $cache_count = $this->get_cache('thread_cache_msg_count');
+        $msg_count = $this->_messagecount($mailbox, 'ALL', TRUE);
+
+        if ($cache_count[$mailbox] == $msg_count) {
+            if ($msg_count == 0)
+                return 1;
+
+            // get highest index
+            $header = iil_C_FetchHeader($this->conn, $mailbox, "$msg_count");
+
+            // uids of highest message matches -> cache seems OK
+            if ($cache_uid[$mailbox] == $header->uid)
+                return 1;
 
+            // cache is invaid
+            return -1;
+        } else {
+            return -1;
+        }
+    }
+
+    function update_thread_cache($mailbox, $thread_tree, $msg_depth, $has_children)
+    {
+        if (empty ($mailbox))
+            return;
+
+        // add to internal (fast) cache
+        $this->cache['__threads'] = array();
+        $this->cache['__threads']['tree'] = $thread_tree;
+        $this->cache['__threads']['depth'] = $msg_depth;
+        $this->cache['__threads']['has_children'] = $has_children;
+
+        // no further caching
+        if (!$this->thread_caching_enabled || true)
+            return;
+
+        $this->db->query("DELETE FROM " .
+                         get_table_name('threads') ."
+                          WHERE user_id = ?
+                          AND mailbox = ?", $_SESSION['user_id'], $mailbox);
+        foreach ($thread_tree as $root => $subtree) {
+            $this->db->query("INSERT INTO " .
+                             get_table_name('threads') . "
+                              (user_id, mailbox, idx, has_children, is_root, root, depth)
+                              VALUES (?, ?, ?, ?, ?, ?, ?)", $_SESSION['user_id'], $mailbox, $root, $has_children[$root] ? 1 : 0, 1, $root, $msg_depth[$root]);
+            $children = array_keys_recursive($subtree);
+            foreach ($children as $idx) {
+                $this->db->query("INSERT INTO " .
+                                 get_table_name('threads') . "
+                                  (user_id, mailbox, idx, has_children, is_root, root, depth)
+                                  VALUES (?, ?, ?, ?, ?, ?, ?)", $_SESSION['user_id'], $mailbox, $idx, $has_children[$idx] ? 1 : 0, 0, $root, $msg_depth[$idx]);
+            }
+        }
+
+        $cache_uid = $this->get_cache('thread_cache_last_uid');
+        $cache_count = $this->get_cache('thread_cache_msg_count');
+        $msg_count = $this->_messagecount($mailbox);
+        if ($msg_count > 0) {
+            $header = iil_C_FetchHeader($this->conn, $mailbox, "$msg_count");
+            $cache_uid[$mailbox] = $header->uid;
+        }
+        $cache_count[$mailbox] = $msg_count;
+        $this->update_cache('thread_cache_last_uid', $cache_uid);
+        $this->update_cache('thread_cache_msg_count', $cache_count);
+    }
+
+    function get_thread_cache_roots($mailbox)
+    {
+        if (!$this->thread_caching_enabled || empty ($mailbox))
+            return array ();
+
+        $cache_key = "threads:$mailbox";
+
+        if ($this->thread_caching_enabled && !isset ($this->cache[$cache_key])) {
+            $this->cache[$cache_key] = array ();
+
+            $sql_result = $this->db->query("SELECT idx
+                                            FROM " .
+                                           get_table_name('threads') . "
+                                            WHERE  user_id=?
+                                            AND    mailbox=?
+                                            AND    is_root", $_SESSION['user_id'], $mailbox);
+
+            while ($sql_arr = $this->db->fetch_array($sql_result))
+                $this->cache[$cache_key][] = $sql_arr[0];
+        }
+
+        return $this->cache[$cache_key];
+    }
+
+    function get_thread_cache_roots_sorted($mailbox, $from, $to, $sort_field, $sort_order)
+    {
+        // empty key -> empty array
+        if (!$this->thread_caching_enabled || !$this->caching_enabled || empty ($mailbox))
+            return array ();
+
+        $cache_key = "threads:$mailbox:$from:$to:$sort_field:$sort_order";
+
+        if ($this->thread_caching_enabled && $this->caching_enabled && !isset ($this->cache[$cache_key])) {
+            $this->cache[$cache_key] = array ();
+
+            $sql_result = $this->db->limitquery("SELECT threads.idx
+                                                 FROM " .
+                                                get_table_name('threads') . "
+                                                 INNER JOIN ".
+                                                get_table_name('messages') . "
+                                                 ON threads.idx = messages.idx
+                                                 AND threads.user_id = messages.user_id
+                                                 WHERE  threads.user_id=?
+                                                 AND    mailbox=?
+                                                 AND    cache_key=?
+                                                 AND    is_root
+                                                 ORDER BY ".$this->db->quoteIdentifier($sort_field)." ".
+                                                 strtoupper($sort_order),
+                                                 $from,
+                                                 $to-$from,
+                                                 $_SESSION['user_id'], $mailbox, $mailbox.'.msg');
+
+            while ($sql_arr = $this->db->fetch_array($sql_result))
+                $this->cache[$cache_key][] = $sql_arr[0];
+        }
+
+        return $this->cache[$cache_key];
+    }
+
+    function get_thread_cache_threads($mailbox, $roots)
+    {
+        // empty key -> empty array
+        if (!$this->thread_caching_enabled || empty ($mailbox))
+            return array ();
+
+        $cache_key = "threads:$mailbox:" . join(',', $roots);
+
+        if ($this->thread_caching_enabled && !isset ($this->cache[$cache_key])) {
+            $this->cache[$cache_key] = array ();
+            // setup the key order according to $roots
+            foreach ($roots as $root)
+                $this->cache[$cache_key][$root] = array();
+
+            $sql_result = $this->db->query("SELECT idx, has_children, root, depth
+                                            FROM " .
+                                           get_table_name('threads') . "
+                                            WHERE  user_id=?
+                                            AND    mailbox=?
+                                            AND    root IN (" . join(',', $roots) .")
+                                            ORDER BY thread_id", $_SESSION['user_id'], $mailbox);
+
+            while ($sql_arr = $this->db->fetch_assoc($sql_result))
+                $this->cache[$cache_key][$sql_arr['root']][] = $sql_arr;
+        }
+
+        return $this->cache[$cache_key];
+    }
 
   /* --------------------------------
    *   encoding/decoding methods
@@ -2899,6 +3176,10 @@ class rcube_imap
     // add incremental value to messagecount
     $a_mailbox_cache[$mailbox][$mode] += $increment;
     
+    // If ALL changes then THREADS may be invalid
+    if ($mode == 'ALL')
+      unset ($a_mailbox_cache[$mailbox]['THREADS']);
+
     // there's something wrong, delete from cache
     if ($a_mailbox_cache[$mailbox][$mode] < 0)
       unset($a_mailbox_cache[$mailbox][$mode]);
@@ -3134,3 +3415,113 @@ function quoted_printable_encode($input, $line_max=76, $space_conv=false)
   }
 
 
+function array_keys_recursive($array)
+{
+    $keys = array ();
+    foreach ($array as $key => $child)
+    {
+        $keys[] = $key;
+        $keys = array_merge($keys, array_keys_recursive($child));
+    }
+    return $keys;
+}
+
+
+/**
+ * Class for sorting a thread tree in a predetermined order.
+ *
+ * @package Mail
+ * @author Chris January
+ */
+class rcube_thread_sorter
+{
+    var $sequence_numbers = array ();
+
+    /**
+     * Set the predetermined sort order.
+     *
+     * @param array Numerically indexed array of IMAP message sequence numbers
+     */
+    function set_sequence_numbers($seqnums)
+    {
+        $this->sequence_numbers = array_flip($seqnums);
+    }
+
+    /**
+     * Sort the array of header objects
+     *
+     * @param threads A thread tree
+     */
+    function sort_threads(& $threads)
+    {
+        uksort($threads, array (
+               $this,
+               "compare_seqnums"
+        ));
+        foreach (array_keys($threads) as $root)
+        {
+            $this->sort_threads($threads[$root]);
+        }
+    }
+
+    /**
+     * Sort method called by uasort()
+     */
+    function compare_seqnums($seqa, $seqb)
+    {
+        // 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;
+
+        // return the relative position as the comparison value
+        return $posa - $posb;
+    }
+}
+
+
+/**
+ * Class for sorting thread roots in a predetermined order.
+ *
+ * @package Mail
+ * @author Chris January
+ */
+class rcube_thread_root_sorter
+{
+    var $sequence_numbers = array ();
+
+    /**
+     * Set the predetermined sort order.
+     *
+     * @param array Numerically indexed array of IMAP message sequence numbers
+     */
+    function set_sequence_numbers($seqnums)
+    {
+        $this->sequence_numbers = array_flip($seqnums);
+    }
+
+    /**
+     * Sort the array of header objects
+     *
+     * @param threads A thread tree
+     */
+    function sort_threads(& $threads)
+    {
+        usort($threads, array (
+              $this,
+              "compare_seqnums"
+        ));
+    }
+
+    /**
+     * Sort method called by uasort()
+     */
+    function compare_seqnums($seqa, $seqb)
+    {
+        // 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;
+
+        // return the relative position as the comparison value
+        return $posa - $posb;
+    }
+}
diff --git a/roundcubemail/program/js/app.js b/roundcubemail/program/js/app.js
index 7f1e7241b..03984427d 100644
--- a/roundcubemail/program/js/app.js
+++ b/roundcubemail/program/js/app.js
@@ -207,7 +207,7 @@ function rcube_webmail()
           }
 
         if (this.env.messagecount)
-          this.enable_command('select-all', 'select-none', 'expunge', true);
+          this.enable_command('select-all', 'select-none', 'expunge', 'expand-all', 'collapse-all', true);
 
         if (this.purge_mailbox_test())
           this.enable_command('purge', true);
@@ -298,7 +298,7 @@ function rcube_webmail()
           this.enable_command('save', true);
           
         if (this.env.action=='folders')
-          this.enable_command('subscribe', 'unsubscribe', 'create-folder', 'rename-folder', 'delete-folder', true);
+          this.enable_command('subscribe', 'unsubscribe', 'create-folder', 'rename-folder', 'delete-folder', 'enable-threading', 'disable-threading', true);
 
         if (this.gui_objects.identitieslist)
           {
@@ -381,6 +381,10 @@ function rcube_webmail()
       row.replied = this.env.messages[uid].replied ? true : false;
       row.flagged = this.env.messages[uid].flagged ? true : false;
       row.forwarded = this.env.messages[uid].forwarded ? true : false;
+      row.has_children = this.env.messages[uid].has_children ? true : false;
+      row.expanded = this.env.messages[uid].expanded ? true : false;
+      row.depth = this.env.messages[uid].depth;
+      row.unread_children = this.env.messages[uid].unread_children;
       }
 
     // set eventhandler to message icon
@@ -397,7 +401,7 @@ function rcube_webmail()
       {
       var found;
       if((found = find_in_array('flag', this.env.coltypes)) >= 0)
-          this.set_env('flagged_col', found+1);
+          this.set_env('flagged_col', found);
       }
 
     // set eventhandler to flag icon, if icon found
@@ -409,6 +413,15 @@ function rcube_webmail()
       row.flagged_icon._row = row.obj;
       row.flagged_icon.onmousedown = function(e) { p.command('toggle_flag', this); };
       }
+      
+    // expando is handled here rather than in rcube_list_widget so that the
+    // expanded state may be persisted in this.env.messages
+    var expando = document.getElementById('rcmexpando' + uid);
+    if (expando != null) 
+      {
+      var p = this;
+      expando.onmousedown = function(e) { return p.expando_clicked(e, uid); };
+      }
   };
 
   // init message compose form: set focus and eventhandlers
@@ -794,6 +807,14 @@ function rcube_webmail()
         this.message_list.clear_selection();
         break;
 
+      case 'expand-all':
+        this.message_list.expand_all();
+        break;
+
+      case 'collapse-all':
+        this.message_list.collapse_all();
+        break;
+
       case 'nextmessage':
         if (this.env.next_uid)
           this.show_message(this.env.next_uid, false, this.env.action=='preview');
@@ -1049,7 +1070,15 @@ function rcube_webmail()
       case 'unsubscribe':
         this.unsubscribe_folder(props);
         break;
-        
+
+      case 'enable-threading':
+        this.enable_threading(props);
+        break;
+
+      case 'disable-threading':
+        this.disable_threading(props);
+        break;
+
       case 'create-folder':
         this.create_folder(props);
         break;
@@ -1976,6 +2005,13 @@ function rcube_webmail()
   };
   
   
+  this.expando_clicked = function(e, id)
+  {
+    this.message_list.expando_clicked(e, id);
+    this.env.messages[id].expanded = this.message_list.rows[id].expanded;
+  },
+  
+  
   /*********************************************************/
   /*********           login form methods          *********/
   /*********************************************************/
@@ -3195,7 +3231,20 @@ function rcube_webmail()
     if (folder)
       this.http_post('unsubscribe', '_mbox='+urlencode(folder));
     };
+
+  this.enable_threading = function(folder)
+    {
+    if (folder)
+      this.http_post('enable-threading', '_mbox='+urlencode(folder));
+    };
+
+  this.disable_threading = function(folder)
+    {
+    if (folder)
+      this.http_post('disable-threading', '_mbox='+urlencode(folder));
+    };
     
+
   // helper method to find a specific mailbox row ID
   this.get_folder_row_id = function(folder)
     {
@@ -3479,7 +3528,7 @@ function rcube_webmail()
     for (var n=0; thead && n<this.coltypes.length; n++) 
       {
       col = this.coltypes[n];
-      if ((cell = thead.rows[0].cells[n+1]) && (col=='from' || col=='to'))
+      if ((cell = thead.rows[0].cells[n]) && (col=='from' || col=='to'))
         {
         // if we have links for sorting, it's a bit more complicated...
         if (cell.firstChild && cell.firstChild.tagName=='A')
@@ -3494,7 +3543,7 @@ function rcube_webmail()
         cell.id = 'rcm'+col;
         }
       else if (col == 'subject' && this.message_list)
-        this.message_list.subject_col = n+1;
+        this.message_list.subject_col = n;
       }
   };
 
@@ -3507,12 +3556,21 @@ function rcube_webmail()
     var tbody = this.gui_objects.messagelist.tBodies[0];
     var rowcount = tbody.rows.length;
     var even = rowcount%2;
+    var depth = cols['depth'];
+    var unread_children = cols['unread_children'];
     
-    this.env.messages[uid] = {deleted:flags.deleted?1:0,
-                              replied:flags.replied?1:0,
-                              unread:flags.unread?1:0,
-			      forwarded:flags.forwarded?1:0,
-                              flagged:flags.flagged?1:0};
+    // don't overwrite the existing values - we want to preserve expanded
+    var message = this.env.messages[uid];
+    if (!message)
+        message = this.env.messages[uid] = Array();
+    message.deleted = flags.deleted?1:0;
+    message.replied = flags.replied?1:0;
+    message.unread = flags.unread?1:0;
+    message.forwarded = flags.forwarded?1:0;
+    message.flagged = flags.flagged?1:0;
+    message.has_children = flags.has_children?1:0;
+    message.unread_children = unread_children;
+    message.depth = depth;
     
     var row = document.createElement('TR');
     row.id = 'rcmrow'+uid;
@@ -3526,7 +3584,9 @@ function rcube_webmail()
       row.className += ' selected';
 
     var icon = this.env.messageicon;
-    if (flags.deleted && this.env.deletedicon)
+    if (!flags.unread && unread_children > 0 && this.env.unreadchildrenicon)
+      icon = this.env.unreadchildrenicon;
+    else if (flags.deleted && this.env.deletedicon)
       icon = this.env.deletedicon;
     else if (flags.replied && this.env.repliedicon)
       {
@@ -3540,10 +3600,17 @@ function rcube_webmail()
     else if(flags.unread && this.env.unreadicon)
       icon = this.env.unreadicon;
     
-    var col = document.createElement('TD');
-    col.className = 'icon';
-    col.innerHTML = icon ? '<img src="'+icon+'" alt="" />' : '';
-    row.appendChild(col);
+    var tree = '';
+    if (depth > 0)
+      {
+      for (var i=1;i<depth;i++)
+        tree += '<div class="branch">&nbsp</div>';
+      tree += flags.has_children?'<div id="rcmexpando' + uid + '" class="' + (message.expanded?'expanded':'collapsed') + '">&nbsp;</div>':'<div class="leaf">&nbsp;</div>';
+      if (depth > 1)
+        row.style.display = 'none';
+      }
+    
+    tree += icon ? '<img src="'+icon+'" alt="" />' : '';
 
     // add each submitted col
     for (var n = 0; n < this.coltypes.length; n++) 
@@ -3552,17 +3619,21 @@ function rcube_webmail()
       col = document.createElement('TD');
       col.className = String(c).toLowerCase();
       
+      var html;
       if (c=='flag')
         {
         if (flags.flagged && this.env.flaggedicon)
-          col.innerHTML = '<img src="'+this.env.flaggedicon+'" alt="" />';
+          html = '<img src="'+this.env.flaggedicon+'" alt="" />';
         else if(!flags.flagged && this.env.unflaggedicon)
-          col.innerHTML = '<img src="'+this.env.unflaggedicon+'" alt="" />';
+          html = '<img src="'+this.env.unflaggedicon+'" alt="" />';
       }
       else if (c=='attachment')
-        col.innerHTML = attachment && this.env.attachmenticon ? '<img src="'+this.env.attachmenticon+'" alt="" />' : '&nbsp;';
+        html = attachment && this.env.attachmenticon ? '<img src="'+this.env.attachmenticon+'" alt="" />' : '&nbsp;';
       else
-        col.innerHTML = cols[c];
+        html = cols[c];
+	  if (n == 0)
+	    html = tree + html;
+      col.innerHTML = html;
 
       row.appendChild(col);
       }
@@ -3578,6 +3649,12 @@ function rcube_webmail()
       }
     };
 
+  // expand any threads that were open
+  this.expand_threads = function()
+    {
+	this.message_list.expand(null);
+    }
+
   // replace content of row count display
   this.set_rowcount = function(text)
     {
@@ -3667,6 +3744,14 @@ function rcube_webmail()
       }
     };
 
+  // replace content of row count display
+  this.set_threaded = function(threaded)
+    {
+    var controls = document.getElementById("threadcontrols");
+    if (controls)
+      controls.style.display = threaded?'inline':'none';
+    };
+
   // notifies that a new message(s) has hit the mailbox
   this.new_message_focus = function()
     {
@@ -3925,7 +4010,8 @@ function rcube_webmail()
             this.show_contentframe(false);
           // disable commands useless when mailbox is empty
           this.enable_command('show', 'reply', 'reply-all', 'forward', 'moveto', 'delete', 'mark', 'viewsource',
-            'print', 'load-attachment', 'purge', 'expunge', 'select-all', 'select-none', 'sort', false);
+            'print', 'load-attachment', 'purge', 'expunge', 'select-all', 'select-none', 'sort', 'expand-all',
+            'collapse-all', false);
         }
         break;
 
@@ -3935,7 +4021,7 @@ function rcube_webmail()
         if (this.task == 'mail') {
           if (this.message_list && request_obj.__action == 'list')
             this.msglist_select(this.message_list);
-          this.enable_command('show', 'expunge', 'select-all', 'select-none', 'sort', (this.env.messagecount > 0));
+          this.enable_command('show', 'expunge', 'select-all', 'select-none', 'sort', 'expand-all', 'collapse-all', (this.env.messagecount > 0));
           this.enable_command('purge', this.purge_mailbox_test());
         }
         else if (this.task == 'addressbook')
@@ -4187,6 +4273,7 @@ function rcube_http_request()
         }
       catch(err)
         {
+        alert(err.stack);
         this.onerror(this);
         this.busy = false;
         }
diff --git a/roundcubemail/program/js/list.js b/roundcubemail/program/js/list.js
index 8d8f9e965..bca1ac9bb 100644
--- a/roundcubemail/program/js/list.js
+++ b/roundcubemail/program/js/list.js
@@ -77,7 +77,7 @@ init: function()
     for(var r=0; r<this.list.tBodies[0].childNodes.length; r++)
     {
       row = this.list.tBodies[0].childNodes[r];
-      while (row && (row.nodeType != 1 || row.style.display == 'none'))
+      while (row && row.nodeType != 1)
       {
         row = row.nextSibling;
         r++;
@@ -118,6 +118,10 @@ init_row: function(row)
     if (document.all)
       row.onselectstart = function() { return false; };
 
+    var expando = document.getElementById('rcmexpando' + uid);
+    if (expando != null)
+      expando.onmousedown = function(e) { return p.expando_clicked(e, uid); };
+
     this.row_init(this.rows[uid]);
   }
 },
@@ -319,6 +323,130 @@ click_row: function(e, id)
 },
 
 
+expando_clicked: function(e, id)
+{
+  var row = this.rows[id];
+  var evtarget = rcube_event.get_target(e);
+  // Don't select this message
+  this.dont_select = true;
+  // Don't treat double click on the expando as double click on the message.
+  row.clicked = 0;
+  if (row.expanded) {
+    evtarget.className = "collapsed";
+    this.collapse(row);
+  } else {
+    evtarget.className = "expanded";
+    this.expand(row);
+  }
+},
+
+
+collapse: function(row)
+{
+    row.expanded = false;
+    var depth = row.depth;
+    var new_row = row ? row.obj.nextSibling : null;
+    var r;
+    while (new_row) {
+        if (new_row.nodeType == 1) {
+            var r = this.rows[new_row.uid];
+            if (r &&r.depth <= depth)
+                break;
+            new_row.style.display = 'none';
+        }
+        new_row = new_row.nextSibling;
+    }
+    return false;
+},
+
+
+expand: function(row)
+{
+    var depth, new_row;
+    if (row) {
+        row.expanded = true;
+        depth = row.depth;
+        new_row = row.obj.nextSibling;
+    } else {
+        var tbody = this.list.tBodies[0];
+        new_row = tbody.firstChild;
+        depth = 0;
+    }
+    var current_expand = true;
+    var current_depth = depth;
+    var expand_stack = new Array();
+    var depth_stack = new Array();
+    while (new_row) {
+        if (new_row.nodeType == 1) {
+            var r = this.rows[new_row.uid];
+            if (r) {
+                if (r.depth <= depth)
+                    break;
+                while (r.depth <= current_depth) {
+                    current_expand = expand_stack.pop();
+                    current_depth = depth_stack.pop();
+                }
+                if (current_expand)
+                     new_row.style.display = 'table-row';
+                if (r.has_children) {
+                    expand_stack.push(current_expand);
+                    depth_stack.push(current_depth);
+                    current_expand = r.expanded;
+                    current_depth = r.depth;
+                }
+            }
+        }
+        new_row = new_row.nextSibling;
+    }
+    return false;
+},
+
+
+collapse_all: function()
+{
+    var tbody = this.list.tBodies[0];
+    new_row = tbody.firstChild;
+    var r;
+    while (new_row) {
+        if (new_row.nodeType == 1) {
+            var r = this.rows[new_row.uid];
+            if (r.depth > 1)
+                new_row.style.display = 'none';
+            if (r.has_children) {
+                r.expanded = false;
+                var expando = document.getElementById('rcmexpando' + r.uid);
+                if (expando)
+                    expando.className = 'collapsed';
+            }
+        }
+        new_row = new_row.nextSibling;
+    }
+    return false;
+},
+
+
+expand_all: function()
+{
+    var tbody = this.list.tBodies[0];
+    new_row = tbody.firstChild;
+    var r;
+    while (new_row) {
+        if (new_row.nodeType == 1) {
+            var r = this.rows[new_row.uid];
+            new_row.style.display = 'table-row';
+            if (r.has_children) {
+                r.expanded = true;
+                var expando = document.getElementById('rcmexpando' + r.uid);
+                if (expando)
+                    expando.className = 'expanded';
+            }
+        }
+        new_row = new_row.nextSibling;
+    }
+    return false;
+},
+
+
 /**
  * get next/previous/last rows that are not hidden
  */
@@ -641,6 +769,12 @@ key_press: function(e)
       // Stop propagation so that the browser doesn't scroll
       rcube_event.cancel(e);
       return this.use_arrow_key(keyCode, mod_key);
+    case 61:
+    case 109:
+    case 32:
+      // Stop propagation
+      rcube_event.cancel(e);
+      return this.use_plusminus_key(keyCode, mod_key);
     default:
       this.shiftkey = e.shiftKey;
       this.key_pressed = keyCode;
@@ -664,6 +798,9 @@ key_down: function(e)
     case 38: 
     case 63233:
     case 63232:
+    case 61:
+    case 109:
+    case 32:
       if (!rcube_event.get_modifier(e) && this.focused)
         return rcube_event.cancel(e);
         
@@ -698,6 +835,28 @@ use_arrow_key: function(keyCode, mod_key)
 
 
 /**
+ * Special handling method for +/- keys
+ */
+use_plusminus_key: function(keyCode, mod_key)
+{
+  var last_selected_row = this.rows[this.last_selected];
+  if (!last_selected_row)
+    return;
+  if (keyCode == 32)
+      keyCode = last_selected_row.expanded ? 109 : 61;
+  if (keyCode == 61)
+      this.expand(last_selected_row);
+  else
+      this.collapse(last_selected_row);
+  var expando = document.getElementById('rcmexpando' + last_selected_row.uid);
+  if (expando)
+    last_selected_row.className = last_selected_row.expanded?'expanded':'collapsed';
+
+  return false;
+},
+
+
+/**
  * Try to scroll the list to make the specified row visible
  */
 scrollto: function(id)
diff --git a/roundcubemail/program/lib/imap.inc b/roundcubemail/program/lib/imap.inc
index 67a2b7b3c..2229f27f0 100644
--- a/roundcubemail/program/lib/imap.inc
+++ b/roundcubemail/program/lib/imap.inc
@@ -182,6 +182,9 @@ class iilBasicHeader
 	var $forwarded = false;
 	var $junk = false;
 	var $flagged = false;
+	var $has_children = false;
+	var $depth = 0;
+	var $unread_children = 0;
 }
 
 /**
@@ -2146,6 +2149,77 @@ function iil_C_ID2UID(&$conn, $folder, $id) {
 	return $result;
 }
 
+function iil_ParseThread($str, $root, $parent, $depth, &$depthmap, &$haschildren) {
+	$node = array();
+	if (strlen($str) == 0)
+		return $node;
+	if (substr($str, 0, 1) != '(') {
+		$p = split('[^0-9]', $str, 2);
+		$msg = $p[0];
+		$str = $p[1];
+		if (is_null($root))
+			$root = $msg;
+		$depthmap[$msg] = $depth;
+		$haschildren[$msg] = false;
+		if (!is_null($parent))
+			$haschildren[$parent] = true;
+		$node[$msg] = iil_ParseThread($str, $root, $msg, $depth + 1, $depthmap, $haschildren);
+	} else {
+		$off = 0;
+		$len = strlen($str);
+		while ($off < $len) {
+			$start = $off;
+			$off++;
+			$n = 1;
+			while ($n > 0) {
+				$p = strpos($str, ')', $off);
+				if ($p === false) {
+					error_log("Can't parse (".substr($str, $off).") - mismatched brackets");
+					return $node;
+				}
+				$p1 = strpos($str, '(', $off);
+				if ($p1 !== false && $p1 < $p) {
+					$off = $p1 + 1;
+					$n++;
+				} else {
+					$off = $p + 1;
+					$n--;
+				}
+			}
+			$s = substr($str, $start + 1, $off - $start - 2); 
+			$node += iil_ParseThread($s, $root, $parent, $depth, $depthmap, $haschildren);			
+		}
+	}
+	
+	return $node;
+}
+
+function iil_C_Thread(&$conn, $folder, $algorithm, $criteria) {
+	$fp = $conn->fp;
+	if (iil_C_Select($conn, $folder)) {
+		$query = 'thrd1 THREAD ' . chop($algorithm). ' UTF-8 ' . chop($criteria);
+		iil_PutLineC($fp, $query);
+		do {
+			$line=trim(iil_ReadLine($fp, 10000));
+			if (eregi("^\* THREAD", $line)) {
+				$str = trim(substr($line, 8));
+				$depthmap = array();
+				$haschildren = array();
+				$tree = iil_ParseThread($str, null, null, 1, $depthmap, $haschildren);
+			}
+		} while (!iil_StartsWith($line, 'thrd1', true));
+
+		$result_code = iil_ParseResult($line);
+		if ($result_code == 0) {
+		    return array($tree, $depthmap, $haschildren);
+		}
+		$conn->error = 'iil_C_Thread: ' . $line . "\n";
+		return false;	
+	}
+	$conn->error = "iil_C_Thread: Couldn't select \"$folder\"\n";
+	return false;
+}
+
 function iil_C_Search(&$conn, $folder, $criteria) {
 	$fp = $conn->fp;
 	if (iil_C_Select($conn, $folder)) {
diff --git a/roundcubemail/program/localization/en_GB/labels.inc b/roundcubemail/program/localization/en_GB/labels.inc
index fae87c558..b46db1528 100644
--- a/roundcubemail/program/localization/en_GB/labels.inc
+++ b/roundcubemail/program/localization/en_GB/labels.inc
@@ -45,6 +45,7 @@ $labels['organization'] = 'Organisation';
 $labels['reply-to'] = 'Reply-To';
 $labels['mailboxlist'] = 'Folders';
 $labels['messagesfromto'] = 'Messages $from to $to of $count';
+$labels['threadsfromto'] = 'Threads $from to $to of $count';
 $labels['messagenrof'] = 'Message $nr of $count';
 $labels['moveto'] = 'Move to...';
 $labels['download'] = 'Download';
@@ -122,6 +123,9 @@ $labels['none'] = 'None';
 $labels['unread'] = 'Unread';
 $labels['flagged'] = 'Flagged';
 $labels['unanswered'] = 'Unanswered';
+$labels['threads'] = 'Threads';
+$labels['expand-all'] = 'Expand All';
+$labels['collapse-all'] = 'Collapse All';
 $labels['filter'] = 'Filter';
 $labels['compact'] = 'Compact';
 $labels['empty'] = 'Empty';
@@ -242,6 +246,7 @@ $labels['2231folding'] = 'Full RFC 2231 (Thunderbird)';
 $labels['miscfolding'] = 'RFC 2047/2231 (MS Outlook)';
 $labels['2047folding'] = 'Full RFC 2047 (other)';
 $labels['advancedoptions'] = 'Advanced options';
+$labels['messagethreading'] = 'Show messages in threads';
 $labels['focusonnewmessage'] = 'Focus browser window on new message';
 $labels['checkallfolders'] = 'Check all folders for new messages';
 $labels['folder'] = 'Folder';
@@ -249,6 +254,7 @@ $labels['folders'] = 'Folders';
 $labels['foldername'] = 'Folder name';
 $labels['subscribed'] = 'Subscribed';
 $labels['messagecount'] = 'Messages';
+$labels['threaded'] = 'Threaded';
 $labels['create'] = 'Create';
 $labels['createfolder'] = 'Create new folder';
 $labels['rename'] = 'Rename';
diff --git a/roundcubemail/program/localization/en_US/labels.inc b/roundcubemail/program/localization/en_US/labels.inc
index 7f0538703..39b145c1b 100644
--- a/roundcubemail/program/localization/en_US/labels.inc
+++ b/roundcubemail/program/localization/en_US/labels.inc
@@ -56,6 +56,7 @@ $labels['reply-to'] = $labels['replyto'];
 
 $labels['mailboxlist'] = 'Folders';
 $labels['messagesfromto'] = 'Messages $from to $to of $count';
+$labels['threadsfromto'] = 'Threads $from to $to of $count';
 $labels['messagenrof'] = 'Message $nr of $count';
 
 $labels['moveto']   = 'Move to...';
@@ -151,6 +152,10 @@ $labels['flagged'] = 'Flagged';
 $labels['unanswered'] = 'Unanswered';
 $labels['filter'] = 'Filter';
 
+$labels['threads'] = 'Threads';
+$labels['expand-all'] = 'Expand All';
+$labels['collapse-all'] = 'Collapse All';
+
 $labels['compact'] = 'Compact';
 $labels['empty'] = 'Empty';
 $labels['purge'] = 'Purge';
@@ -297,6 +302,7 @@ $labels['2231folding'] = 'Full RFC 2231 (Thunderbird)';
 $labels['miscfolding'] = 'RFC 2047/2231 (MS Outlook)';
 $labels['2047folding'] = 'Full RFC 2047 (other)';
 $labels['advancedoptions'] = 'Advanced options';
+$labels['messagethreading'] = 'Show messages in threads';
 $labels['focusonnewmessage'] = 'Focus browser window on new message';
 $labels['checkallfolders'] = 'Check all folders for new messages';
 
@@ -305,6 +311,7 @@ $labels['folders']  = 'Folders';
 $labels['foldername']  = 'Folder name';
 $labels['subscribed']  = 'Subscribed';
 $labels['messagecount'] = 'Messages';
+$labels['threaded'] = 'Threaded';
 $labels['create']  = 'Create';
 $labels['createfolder']  = 'Create new folder';
 $labels['rename'] = 'Rename';
diff --git a/roundcubemail/program/steps/mail/check_recent.inc b/roundcubemail/program/steps/mail/check_recent.inc
index a0668537d..d13eef163 100644
--- a/roundcubemail/program/steps/mail/check_recent.inc
+++ b/roundcubemail/program/steps/mail/check_recent.inc
@@ -28,9 +28,9 @@ foreach ($a_mailboxes as $mbox_name) {
       // refresh saved search set
       if (($search_request = get_input_value('_search', RCUBE_INPUT_GPC)) && isset($_SESSION['search'][$search_request])) {
         $_SESSION['search'][$search_request] = $IMAP->refresh_search();
-        $all_count = $IMAP->messagecount();
+        $all_count = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
       } else {
-        $all_count = $IMAP->messagecount(NULL, 'ALL', TRUE);
+        $all_count = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL', TRUE);
       }
       
       $unread_count = $IMAP->messagecount(NULL, 'UNSEEN', TRUE);
@@ -51,18 +51,24 @@ foreach ($a_mailboxes as $mbox_name) {
       if (empty($_GET['_list']))
         continue;
 
-      // use SEARCH/SORT to find recent messages
-      $search_str = 'RECENT';
-      if ($search_request)
-        $search_str .= ' '.$IMAP->search_string;
-
-      $result = $IMAP->search($mbox_name, $search_str, NULL, 'date');
+      if (rcmail::get_instance()->imap->threading) {
+          $OUTPUT->command('message_list.clear');
+          $sort_col   = isset($_SESSION['sort_col'])   ? $_SESSION['sort_col']   : $CONFIG['message_sort_col'];
+          $sort_order = isset($_SESSION['sort_order']) ? $_SESSION['sort_order'] : $CONFIG['message_sort_order'];
+          $result_h = $IMAP->list_headers($mbox_name, NULL, $sort_col, $sort_order);
+          // add to the list
+          rcmail_js_message_list($result_h);
+      } else {
+          // use SEARCH/SORT to find recent messages
+          $search_str = 'RECENT';
+          if ($search_request)
+              $search_str .= ' '.$IMAP->search_string;
 
-      if ($result) {
-        // get the headers
-        $result_h = $IMAP->list_headers($mbox_name, 1, 'date', 'DESC');
-        // add to the list
-        rcmail_js_message_list($result_h, TRUE);
+          $result = $IMAP->search($mbox_name, $search_str, NULL, 'date');
+          // get the headers
+          $result_h = $IMAP->list_headers($mbox_name, 1, 'date', 'DESC');
+          // add to the list
+          rcmail_js_message_list($result_h, TRUE);
       }
     }
   }
diff --git a/roundcubemail/program/steps/mail/func.inc b/roundcubemail/program/steps/mail/func.inc
index 79e148d8a..bac49463e 100644
--- a/roundcubemail/program/steps/mail/func.inc
+++ b/roundcubemail/program/steps/mail/func.inc
@@ -44,6 +44,8 @@ if ($mbox = get_input_value('_mbox', RCUBE_INPUT_GPC))
   $IMAP->set_mailbox(($_SESSION['mbox'] = $mbox));
 else
   $_SESSION['mbox'] = $IMAP->get_mailbox_name();
+$a_message_threading = $RCMAIL->config->get('message_threading', array());
+rcmail::get_instance()->imap->threading = $a_message_threading[$_SESSION['mbox']];
 
 if (!empty($_GET['_page']))
   $IMAP->set_page(($_SESSION['page'] = intval($_GET['_page'])));
@@ -80,7 +82,7 @@ if (empty($RCMAIL->action) || $RCMAIL->action == 'list')
       }
     
       // make sure the message count is refreshed (for default view)
-      $IMAP->messagecount($mbox_name, 'ALL', true);
+      $IMAP->messagecount($mbox_name, rcmail::get_instance()->imap->threading?'THREADS':'ALL', true);
     }
 	
   // set current mailbox in client environment
@@ -152,7 +154,6 @@ function rcmail_message_list($attrib)
   
   // add col definition
   $out .= '<colgroup>';
-  $out .= '<col class="icon" />';
 
   foreach ($a_show_cols as $col)
     $out .= ($col!='attachment') ? sprintf('<col class="%s" />', $col) : '<col class="icon" />';
@@ -160,7 +161,7 @@ function rcmail_message_list($attrib)
   $out .= "</colgroup>\n";
 
   // add table title
-  $out .= "<thead><tr>\n<td class=\"icon\">&nbsp;</td>\n";
+  $out .= "<thead><tr>\n";
 
   $javascript = '';
   foreach ($a_show_cols as $col)
@@ -257,9 +258,15 @@ function rcmail_message_list($attrib)
       $js_row_arr['forwarded'] = true;
     if ($header->flagged)
       $js_row_arr['flagged'] = true;
+    if ($header->has_children)
+      $js_row_arr['has_children'] = true;
+    $js_row_arr['depth'] = $header->depth;
+    $js_row_arr['unread_children'] = $header->unread_children;
 
-    // set message icon  
-    if ($attrib['deletedicon'] && $header->deleted)
+    // set message icon
+    if ($header->seen && $attrib['unreadchildrenicon'] && $header->unread_children > 0) 
+      $message_icon = $attrib['unreadchildrenicon'];
+    else if ($attrib['deletedicon'] && $header->deleted)
       $message_icon = $attrib['deletedicon'];
     else if ($attrib['repliedicon'] && $header->answered)
       {
@@ -284,19 +291,28 @@ function rcmail_message_list($attrib)
     if ($attrib['attachmenticon'] && preg_match("/multipart\/m/i", $header->ctype))
       $attach_icon = $attrib['attachmenticon'];
         
-    $out .= sprintf('<tr id="rcmrow%d" class="message%s%s%s%s">'."\n",
+    $out .= sprintf('<tr id="rcmrow%d" class="message%s%s%s%s"%s>'."\n",
                     $header->uid,
                     $header->seen ? '' : ' unread',
                     $header->deleted ? ' deleted' : '',
                     $header->flagged ? ' flagged' : '',
-                    $zebra_class);
+                    $zebra_class,
+                    ($header->depth  > 1) ? ' style="display: none"' : '');
     
-    $out .= sprintf("<td class=\"icon\">%s</td>\n", $message_icon ? sprintf($image_tag, $skin_path, $message_icon, '') : '');
-
+    $tree = '';
+    $depth = $header->depth;
+    if ($depth > 0)
+      {
+      for ($i=1;$i<$depth;$i++)
+        $tree .= '<div class="branch">&nbsp</div>';
+      $tree .= $header->has_children?'<div id="rcmexpando' . $header->uid . '" class="collapsed">&nbsp;</div>':'<div class="leaf">&nbsp;</div>';
+      }
+    $tree .= $message_icon ? sprintf($image_tag, $skin_path, $message_icon, '') : '';
 
     $IMAP->set_charset(!empty($header->charset) ? $header->charset : $CONFIG['default_charset']);
   
     // format each col
+    $first = true;
     foreach ($a_show_cols as $col)
       {
       if ($col=='from' || $col=='to')
@@ -318,6 +334,10 @@ function rcmail_message_list($attrib)
       else
         $cont = Q($header->$col);
         
+      if ($first) {
+      	$first = false;
+      	$cont = $tree . $cont;
+      }
       if ($col!='attachment')
         $out .= '<td class="'.$col.'">' . $cont . "</td>\n";
       else
@@ -333,7 +353,7 @@ function rcmail_message_list($attrib)
   // complete message table
   $out .= "</tbody></table>\n";
   
-  $message_count = $IMAP->messagecount();
+  $message_count = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
   
   // set client env
   $OUTPUT->add_gui_object('mailcontframe', 'mailcontframe');
@@ -362,6 +382,8 @@ function rcmail_message_list($attrib)
     $OUTPUT->set_env('flaggedicon', $skin_path . $attrib['flaggedicon']);
   if ($attrib['unflaggedicon'])
     $OUTPUT->set_env('unflaggedicon', $skin_path . $attrib['unflaggedicon']);
+  if ($attrib['unreadchildrenicon'])
+    $OUTPUT->set_env('unreadchildrenicon', $skin_path . $attrib['unreadchildrenicon']);
   
   $OUTPUT->set_env('messages', $a_js_message_arr);
   $OUTPUT->set_env('coltypes', $a_show_cols);
@@ -393,6 +415,12 @@ function rcmail_js_message_list($a_headers, $insert_top=FALSE)
 
   $OUTPUT->command('set_message_coltypes', $a_show_cols);
 
+  // remove 'attachment' and 'flag' columns, we don't need them here
+  if(($key = array_search('attachment', $a_show_cols)) !== FALSE)
+    unset($a_show_cols[$key]);
+  if(($key = array_search('flag', $a_show_cols)) !== FALSE)
+    unset($a_show_cols[$key]);
+
   // loop through message headers
   foreach ($a_headers as $n => $header)
     {
@@ -404,12 +432,6 @@ function rcmail_js_message_list($a_headers, $insert_top=FALSE)
 
     $IMAP->set_charset(!empty($header->charset) ? $header->charset : $CONFIG['default_charset']);
 
-    // remove 'attachment' and 'flag' columns, we don't need them here
-    if(($key = array_search('attachment', $a_show_cols)) !== FALSE)
-      unset($a_show_cols[$key]);
-    if(($key = array_search('flag', $a_show_cols)) !== FALSE)
-      unset($a_show_cols[$key]);
-
     // format each col; similar as in rcmail_message_list()
     foreach ($a_show_cols as $col)
       {
@@ -438,6 +460,9 @@ function rcmail_js_message_list($a_headers, $insert_top=FALSE)
     $a_msg_flags['replied'] = $header->answered ? 1 : 0;
     $a_msg_flags['forwarded'] = $header->forwarded ? 1 : 0;
     $a_msg_flags['flagged'] = $header->flagged ? 1 : 0;
+    $a_msg_flags['has_children'] = $header->has_children ? 1 : 0;
+    $a_msg_cols['depth'] = $header->depth;
+    $a_msg_cols['unread_children'] = $header->unread_children;
     
     $OUTPUT->command('add_message_row',
       $header->uid,
@@ -446,6 +471,7 @@ function rcmail_js_message_list($a_headers, $insert_top=FALSE)
       preg_match("/multipart\/m/i", $header->ctype),
       $insert_top);
     }
+  $OUTPUT->command('expand_threads');
   }
 
 
@@ -569,19 +595,19 @@ function rcmail_get_messagecount_text($count=NULL, $page=NULL)
     {
     return rcube_label(array('name' => 'messagenrof',
                              'vars' => array('nr'  => $MESSAGE->index+1,
-                                             'count' => $count!==NULL ? $count : $IMAP->messagecount())));
+                                             'count' => $count!==NULL ? $count : $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL'))));
     }
 
   if ($page===NULL)
     $page = $IMAP->list_page;
     
   $start_msg = ($page-1) * $IMAP->page_size + 1;
-  $max = $count!==NULL ? $count : $IMAP->messagecount();
+  $max = $count!==NULL ? $count : $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
 
   if ($max==0)
     $out = rcube_label('mailboxempty');
   else
-    $out = rcube_label(array('name' => 'messagesfromto',
+    $out = rcube_label(array('name' => rcmail::get_instance()->imap->threading?'threadsfromto':'messagesfromto',
                               'vars' => array('from'  => $start_msg,
                                               'to'    => min($max, $start_msg + $IMAP->page_size - 1),
                                               'count' => $max)));
diff --git a/roundcubemail/program/steps/mail/list.inc b/roundcubemail/program/steps/mail/list.inc
index 5cc2a574d..4d5169c29 100644
--- a/roundcubemail/program/steps/mail/list.inc
+++ b/roundcubemail/program/steps/mail/list.inc
@@ -53,10 +53,10 @@ if ($_SESSION['search_filter'] && $_SESSION['search_filter'] != 'ALL')
 			      
 
 // fetch message headers
-if ($IMAP->messagecount($mbox_name, 'ALL', !empty($_REQUEST['_refresh'])))
+if ($IMAP->messagecount($mbox_name, rcmail::get_instance()->imap->threading?'THREADS':'ALL', !empty($_REQUEST['_refresh'])))
   $a_headers = $IMAP->list_headers($mbox_name, NULL, $sort_col, $sort_order);
 
-$count = $IMAP->messagecount($mbox_name);
+$count = $IMAP->messagecount($mbox_name, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
 $unseen = $IMAP->messagecount($mbox_name, 'UNSEEN', !empty($_REQUEST['_refresh']));
 
 // update message count display
@@ -65,6 +65,7 @@ $OUTPUT->set_env('messagecount', $count);
 $OUTPUT->set_env('pagecount', $pages);
 $OUTPUT->command('set_rowcount', rcmail_get_messagecount_text($count));
 $OUTPUT->command('set_mailboxname', rcmail_get_mailbox_name_text());
+$OUTPUT->command('set_threaded', rcmail::get_instance()->imap->threading);
 
 // add message rows
 if (isset($a_headers) && count($a_headers))
diff --git a/roundcubemail/program/steps/mail/move_del.inc b/roundcubemail/program/steps/mail/move_del.inc
index 673bd800b..bf78429f1 100644
--- a/roundcubemail/program/steps/mail/move_del.inc
+++ b/roundcubemail/program/steps/mail/move_del.inc
@@ -20,7 +20,7 @@
 */
 
 // count messages before changing anything
-$old_count = $IMAP->messagecount();
+$old_count = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
 $old_pages = ceil($old_count / $IMAP->page_size);
 
 // move messages
@@ -71,7 +71,7 @@ if (($search_request = get_input_value('_search', RCUBE_INPUT_GPC)) && $IMAP->se
     $_SESSION['search'][$search_request] = $IMAP->refresh_search();
 }
 
-$msg_count      = $IMAP->messagecount();
+$msg_count      = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
 $pages          = ceil($msg_count / $IMAP->page_size);
 $nextpage_count = $old_count - $IMAP->page_size * $IMAP->list_page;
 $remaining      = $msg_count - $IMAP->page_size * ($IMAP->list_page - 1);
@@ -90,7 +90,6 @@ $OUTPUT->set_env('current_page', $IMAP->list_page);
 $OUTPUT->command('set_rowcount', rcmail_get_messagecount_text($msg_count));
 
 // update mailboxlist
-$mbox = $IMAP->get_mailbox_name();
 $OUTPUT->command('set_unread_count', $mbox, $IMAP->messagecount($mbox, 'UNSEEN'), ($mbox == 'INBOX'));
 
 if ($RCMAIL->action=='moveto' && $target) {
@@ -106,7 +105,11 @@ if ($addrows && $_POST['_from']!='show' && ($jump_back || $nextpage_count > 0))
   
     $a_headers = $IMAP->list_headers($mbox, NULL, $sort_col, $sort_order);
     if (!$jump_back) {
-        $a_headers = array_slice($a_headers, -$count, $count);
+        if ($_SESSION['threads'])
+          // TODO: count number of roots deleted and slice that many roots from the end of $a_headers 
+          $OUTPUT->command('message_list.clear');
+        else
+          $a_headers = array_slice($a_headers, -$count, $count);
     }
     rcmail_js_message_list($a_headers);
 }
diff --git a/roundcubemail/program/steps/mail/rss.inc b/roundcubemail/program/steps/mail/rss.inc
index 72317c68f..4e75811c9 100644
--- a/roundcubemail/program/steps/mail/rss.inc
+++ b/roundcubemail/program/steps/mail/rss.inc
@@ -42,7 +42,7 @@ if (dirname($_SERVER['SCRIPT_NAME']) != '/')
 $webmail_url .= '?_task=mail';
 
 $messagecount_unread = $IMAP->messagecount('INBOX', 'UNSEEN', TRUE);
-$messagecount = $IMAP->messagecount();
+$messagecount = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
 
 $sort_col = 'date';
 $sort_order = 'DESC';
diff --git a/roundcubemail/program/steps/mail/search.inc b/roundcubemail/program/steps/mail/search.inc
index 95ca67a12..d74a23030 100644
--- a/roundcubemail/program/steps/mail/search.inc
+++ b/roundcubemail/program/steps/mail/search.inc
@@ -90,7 +90,7 @@ if ($search_str)
 
 // Get the headers
 $result_h = $IMAP->list_headers($mbox, 1, $_SESSION['sort_col'], $_SESSION['sort_order']);
-$count = $IMAP->messagecount();
+$count = $IMAP->messagecount(NULL, rcmail::get_instance()->imap->threading?'THREADS':'ALL');
 
 // save search results in session
 if (!is_array($_SESSION['search']))
diff --git a/roundcubemail/program/steps/settings/func.inc b/roundcubemail/program/steps/settings/func.inc
index d0a3ae69c..6515ae4f6 100644
--- a/roundcubemail/program/steps/settings/func.inc
+++ b/roundcubemail/program/steps/settings/func.inc
@@ -168,6 +168,8 @@ function rcmail_user_prefs_block($part, $no_override, $attrib)
   case 'mailbox':
     $table = new html_table(array('cols' => 2));
 
+    $RCMAIL->imap_init(true);
+
     if (!isset($no_override['focus_on_new_message'])) {
       $field_id = 'rcmfd_focus_on_new_message';
       $input_focus_on_new_message = new html_checkbox(array('name' => '_focus_on_new_message', 'id' => $field_id, 'value' => 1));
diff --git a/roundcubemail/program/steps/settings/manage_folders.inc b/roundcubemail/program/steps/settings/manage_folders.inc
index 9affded98..80a6b7c65 100644
--- a/roundcubemail/program/steps/settings/manage_folders.inc
+++ b/roundcubemail/program/steps/settings/manage_folders.inc
@@ -38,6 +38,28 @@ else if ($RCMAIL->action=='unsubscribe')
     $IMAP->unsubscribe(array($mbox));
   }
 
+// enable threading for one or more mailboxes
+else if ($RCMAIL->action=='enable-threading')
+  {
+  if ($mbox = get_input_value('_mbox', RCUBE_INPUT_POST, false, 'UTF-7'))
+    $a_user_prefs = $USER->get_prefs();
+    if (!is_array($a_user_prefs['message_threading']))
+      $a_user_prefs['message_threading'] = array();
+    $a_user_prefs['message_threading'][$mbox] = true;
+    $USER->save_prefs($a_user_prefs);
+  }
+
+// enable threading for one or more mailboxes
+else if ($RCMAIL->action=='disable-threading')
+  {
+  if ($mbox = get_input_value('_mbox', RCUBE_INPUT_POST, false, 'UTF-7'))
+    $a_user_prefs = $USER->get_prefs();
+    if (!is_array($a_user_prefs['message_threading']))
+      $a_user_prefs['message_threading'] = array();
+    unset($a_user_prefs['message_threading'][$mbox]);
+    $USER->save_prefs($a_user_prefs);
+  }
+
 // create a new mailbox
 else if ($RCMAIL->action=='create-folder')
   {
@@ -162,6 +184,8 @@ function rcube_subscription_form($attrib)
   {
   global $IMAP, $CONFIG, $OUTPUT;
 
+  $threading_supported = $IMAP->get_capability('thread=references');
+
   list($form_start, $form_end) = get_form_tags($attrib, 'folders');
   unset($attrib['form']);
   
@@ -174,6 +198,8 @@ function rcube_subscription_form($attrib)
   $table->add_header('name', rcube_label('foldername'));
   $table->add_header('msgcount', rcube_label('messagecount'));
   $table->add_header('subscribed', rcube_label('subscribed'));
+  if ($threading_supported)
+    $table->add_header('threaded', rcube_label('threaded'));
   $table->add_header('rename', '&nbsp;');
   $table->add_header('delete', '&nbsp;');
 
@@ -183,6 +209,7 @@ function rcube_subscription_form($attrib)
 
   $a_unsubscribed = $IMAP->list_unsubscribed();
   $a_subscribed = $IMAP->list_mailboxes();
+  $a_threaded =rcmail::get_instance()->config->get('message_threading', array()); 
   $delimiter = $IMAP->get_hierarchy_delimiter();
   $a_js_folders = $seen_folders = $list_folders = array();
 
@@ -212,6 +239,10 @@ function rcube_subscription_form($attrib)
     'name' => '_subscribed[]',
     'onclick' => JS_OBJECT_NAME.".command(this.checked?'subscribe':'unsubscribe',this.value)",
   ));
+  $checkbox_threaded = new html_checkbox(array(
+    'name' => '_threaded[]',
+    'onclick' => JS_OBJECT_NAME.".command(this.checked?'enable-threading':'disable-threading',this.value)",
+  ));
   
   if (!empty($attrib['deleteicon']))
     $del_button = html::img(array('src' => $CONFIG['skin_path'] . $attrib['deleteicon'], 'alt' => rcube_label('delete')));
@@ -227,6 +258,7 @@ function rcube_subscription_form($attrib)
   foreach ($list_folders as $i => $folder) {
     $idx = $i + 1;
     $subscribed = in_array($folder['id'], $a_subscribed);
+    $threaded = $a_threaded[$folder['id']];
     $protected = ($CONFIG['protect_default_folders'] == true && in_array($folder['id'], $CONFIG['default_imap_folders']));
     $classes = array($i%2 ? 'even' : 'odd');
     $folder_js = JQ($folder['id']);
@@ -239,9 +271,13 @@ function rcube_subscription_form($attrib)
     $table->add_row(array('id' => 'rcmrow'.$idx, 'class' => join(' ', $classes)));
     
     $table->add('name', Q($display_folder));
-    $table->add('msgcount', ($folder['virtual'] ? '' : $IMAP->messagecount($folder['id'])));
+    $table->add('msgcount', ($folder['virtual'] ? '' : $IMAP->messagecount($folder['id']))); // XXX: Use THREADS or ALL?
     $table->add('subscribed', ($protected || $folder['virtual']) ? ($subscribed ? '&nbsp;&#x2022;' : '&nbsp;') :
         $checkbox_subscribe->show(($subscribed ? $folder_utf8 : ''), array('value' => $folder_utf8)));
+    if ($IMAP->get_capability('thread=references')) {
+      $table->add('threaded',
+                  $checkbox_threaded->show(($threaded ? $folder_utf8 : ''), array('value' => $folder_utf8)));
+    }
     
     // add rename and delete buttons
     if (!$protected && !$folder['virtual']) {