diff --git a/plugins/kolab_auth/kolab_auth_ldap.php b/plugins/kolab_auth/kolab_auth_ldap.php
index 3a83d10e..4584c60b 100644
--- a/plugins/kolab_auth/kolab_auth_ldap.php
+++ b/plugins/kolab_auth/kolab_auth_ldap.php
@@ -391,17 +391,11 @@ class kolab_auth_ldap extends rcube_ldap_generic
                 list($usr, $dom) = explode('@', $user);
 
                 // unrealm domain, user login can contain a domain alias
-                if ($dom != $domain && ($r_domain = $this->find_domain($dom))) {
-                    // $dom is a domain DN string?
-                    if (strpos($r_domain, '=')) {
-                        $dc = $r_domain;
-                    }
-                    else {
-                        $dc = 'dc=' . implode(',dc=', explode('.', $r_domain));
-                    }
+                if ($dom != $domain && ($dc = $this->find_domain($dom))) {
+                    // @FIXME: we should replace domain in $user, I suppose
                 }
             }
-            else if ($domain && !strpos($user, '@')) {
+            else if ($domain) {
                 $user .= '@' . $domain;
             }
 
@@ -426,7 +420,7 @@ class kolab_auth_ldap extends rcube_ldap_generic
      *
      * @param string $domain Domain name
      *
-     * @return string Domain name or domain DN string
+     * @return string Domain DN string
      */
     function find_domain($domain)
     {
@@ -458,7 +452,9 @@ class kolab_auth_ldap extends rcube_ldap_generic
                 return $entry['inetdomainbasedn'];
             }
 
-            return is_array($entry[$name_attr]) ? 'dc=' . implode(',dc=', explode('.', $entry[$name_attr][0])) : 'dc=' . implode(',dc=', explode('.', $entry[$name_attr]));
+            $domain = is_array($entry[$name_attr]) ? $entry[$name_attr][0] : $entry[$name_attr];
+
+            return $domain ? 'dc=' . implode(',dc=', explode('.', $domain)) : null;
         }
     }