Index: roundcubemail/config/main.inc.php.dist
===================================================================
--- roundcubemail/config/main.inc.php.dist	(revision 2308)
+++ roundcubemail/config/main.inc.php.dist	(working copy)
@@ -374,6 +374,9 @@
 // default setting if preview pane is enabled
 $rcmail_config['preview_pane'] = FALSE;
 
+// show messages in threads
+$rcmail_config['message_threading'] = false;
+
 // focus new window if new message arrives
 $rcmail_config['focus_on_new_message'] = true;
 
Index: roundcubemail/program/steps/settings/func.inc
===================================================================
--- roundcubemail/program/steps/settings/func.inc	(revision 2308)
+++ roundcubemail/program/steps/settings/func.inc	(working copy)
@@ -168,6 +168,13 @@
   case 'mailbox':
     $table = new html_table(array('cols' => 2));
 
+    if (!isset($no_override['message_threading'])) {
+      $field_id = 'rcmfd_message_threading';
+      $input_message_threading = new html_checkbox(array('name' => '_message_threading', 'id' => $field_id, 'value' => 1));
+      $table->add('title', html::label($field_id, Q(rcube_label('messagethreading'))));
+      $table->add(null, $input_message_threading->show($config['message_threading']?1:0));
+    }
+
     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' => $field_id, 'value' => 1));
Index: roundcubemail/program/steps/settings/save_prefs.inc
===================================================================
--- roundcubemail/program/steps/settings/save_prefs.inc	(revision 2308)
+++ roundcubemail/program/steps/settings/save_prefs.inc	(working copy)
@@ -29,6 +29,7 @@
   'htmleditor'   => isset($_POST['_htmleditor']) ? TRUE : FALSE,
   'inline_images'   => isset($_POST['_inline_images']) ? TRUE : FALSE,
   'preview_pane' => isset($_POST['_preview_pane']) ? TRUE : FALSE,
+  'message_threading' => isset($_POST['_message_threading']) ? TRUE : FALSE,
   'focus_on_new_message' => isset($_POST['_focus_on_new_message']) ? TRUE : FALSE,
   'read_when_deleted' => isset($_POST['_read_when_deleted']) ? TRUE : FALSE,
   'skip_deleted' => isset($_POST['_skip_deleted']) ? TRUE : FALSE,