diff --git a/lib/drivers/kolab/kolab_file_autocomplete.php b/lib/drivers/kolab/kolab_file_autocomplete.php
index dc4b197..b710cbc 100644
--- a/lib/drivers/kolab/kolab_file_autocomplete.php
+++ b/lib/drivers/kolab/kolab_file_autocomplete.php
@@ -1,171 +1,221 @@
 <?php
 /*
  +--------------------------------------------------------------------------+
  | This file is part of the Kolab File API                                  |
  |                                                                          |
  | Copyright (C) 2012-2018, Kolab Systems AG                                |
  |                                                                          |
  | This program is free software: you can redistribute it and/or modify     |
  | it under the terms of the GNU Affero General Public License as published |
  | by the Free Software Foundation, either version 3 of the License, or     |
  | (at your option) any later version.                                      |
  |                                                                          |
  | This program is distributed in the hope that it will be useful,          |
  | but WITHOUT ANY WARRANTY; without even the implied warranty of           |
  | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the             |
  | GNU Affero General Public License for more details.                      |
  |                                                                          |
  | You should have received a copy of the GNU Affero General Public License |
  | along with this program. If not, see <http://www.gnu.org/licenses/>      |
  +--------------------------------------------------------------------------+
  | Author: Aleksander Machniak <machniak@kolabsys.com>                      |
  +--------------------------------------------------------------------------+
 */
 
 class kolab_file_autocomplete
 {
     private $rc;
     private $ldap;
 
     /**
      * Class constructor
      */
     public function __construct()
     {
         $this->rc = rcube::get_instance();
     }
 
     /**
      * Search users/groups
      */
     public function search($search, $with_groups = false)
     {
         if (!$this->init_ldap()) {
             return false;
         }
 
         $max  = (int) $this->rc->config->get('autocomplete_max', 15);
         $mode = (int) $this->rc->config->get('addressbook_search_mode');
         $me   = $this->rc->get_user_name();
 
         $this->ldap->set_pagesize($max);
 
         $result = $this->ldap->search('*', $search, $mode);
         $users  = array();
         $index  = array();
 
         foreach ($result->records as $record) {
             $user = $record['uid'];
 
             if (is_array($user)) {
                 $user = array_filter($user);
                 $user = $user[0];
             }
 
             if (in_array($me, rcube_addressbook::get_col_values('email', $record, true))) {
                 continue;
             }
 
             if ($user) {
                 $display = rcube_addressbook::compose_search_name($record);
                 $user    = array('name' => $user, 'display' => $display);
                 $users[] = $user;
                 $index[] = $display ?: $user['name'];
             }
         }
 
         $group_support = $this->rc->config->get('fileapi_groups');
         $group_prefix  = $this->rc->config->get('fileapi_group_prefix');
         $group_field   = $this->rc->config->get('fileapi_group_field', 'name');
 
         if ($with_groups && $group_support && $group_field) {
             $result = $this->ldap->list_groups($search, $mode);
 
             foreach ($result as $record) {
                 $group    = $record['name'];
                 $group_id = is_array($record[$group_field]) ? $record[$group_field][0] : $record[$group_field];
 
                 if ($group) {
                     $users[] = array('name' => ($group_prefix ? $group_prefix : '') . $group_id, 'display' => $group, 'type' => 'group');
                     $index[] = $group;
                 }
             }
         }
 
         if (count($users)) {
             array_multisort($index, SORT_ASC, SORT_LOCALE_STRING, $users);
         }
 
         if (count($users) > $max) {
             $users = array_slice($users, 0, $max);
         }
 
         return $users;
     }
 
+    /**
+     * Resolve acl identifier to user/group name
+     */
+    public function resolve_uid($id, &$title = null)
+    {
+        $groups      = $this->rc->config->get('acl_groups');
+        $prefix      = $this->rc->config->get('acl_group_prefix');
+        $group_field = $this->rc->config->get('acl_group_field', 'name');
+
+        if ($groups && $prefix && strpos($id, $prefix) === 0) {
+            $gid = substr($id, strlen($prefix));
+
+            // Unfortunately this works only if group_field=name,
+            // list_groups() allows searching by group name only
+            if ($group_field === 'name' && $this->init_ldap()) {
+                $result = $this->ldap->list_groups($gid, rcube_addressbook::SEARCH_STRICT);
+
+                if (count($result) === 1 && ($record = $result[0])) {
+                    if ($record[$group_field] === $gid) {
+                        $display = $record['name'];
+                        if ($display != $gid) {
+                            $title = sprintf('%s (%s)', $display, $gid);
+                        }
+
+                        return $display;
+                    }
+                }
+            }
+
+            return $gid;
+        }
+
+        if ($this->init_ldap()) {
+            $this->ldap->set_pagesize('2');
+            // Note: 'uid' works here because we overwrite fieldmap in init_ldap() above
+            $result = $this->ldap->search('uid', $id, rcube_addressbook::SEARCH_STRICT);
+
+            if ($result->count === 1 && ($record = $result->first())) {
+                if ($record['uid'] === $id) {
+                    $title   = rcube_addressbook::compose_search_name($record);
+                    $display = rcube_addressbook::compose_list_name($record);
+
+                    return $display;
+                }
+            }
+        }
+
+        return $id;
+    }
+
     /**
      * Initializes autocomplete LDAP backend
      */
     private function init_ldap()
     {
         if ($this->ldap) {
             return $this->ldap->ready;
         }
 
         // get LDAP config
         $config = $this->rc->config->get('fileapi_users_source');
 
         if (empty($config)) {
             return false;
         }
 
         // not an array, use configured ldap_public source
         if (!is_array($config)) {
             $ldap_config = (array) $this->rc->config->get('ldap_public');
             $config      = $ldap_config[$config];
         }
 
         $uid_field = $this->rc->config->get('fileapi_users_field', 'mail');
         $filter    = $this->rc->config->get('fileapi_users_filter');
         $debug     = $this->rc->config->get('ldap_debug');
         $domain    = $this->rc->config->mail_domain($_SESSION['imap_host']);
 
         if (empty($uid_field) || empty($config)) {
             return false;
         }
 
         // get name attribute
         if (!empty($config['fieldmap'])) {
             $name_field = $config['fieldmap']['name'];
         }
         // ... no fieldmap, use the old method
         if (empty($name_field)) {
             $name_field = $config['name_field'];
         }
 
         // add UID field to fieldmap, so it will be returned in a record with name
         $config['fieldmap']['name'] = $name_field;
         $config['fieldmap']['uid']  = $uid_field;
 
         // search in UID and name fields
         // $name_field can be in a form of <field>:<modifier> (#1490591)
         $name_field = preg_replace('/:.*$/', '', $name_field);
         $search     = array_unique(array($name_field, $uid_field));
 
         $config['search_fields']   = $search;
         $config['required_fields'] = array($uid_field);
 
         // set search filter
         if ($filter) {
             $config['filter'] = $filter;
         }
 
         // disable vlv
         $config['vlv'] = false;
 
         // Initialize LDAP connection
         $this->ldap = new rcube_ldap($config, $debug, $domain);
 
         return $this->ldap->ready;
     }
 }