diff --git a/data/web/inc/functions.mailbox.inc.php b/data/web/inc/functions.mailbox.inc.php
index af4f4be7..18db3fa9 100644
--- a/data/web/inc/functions.mailbox.inc.php
+++ b/data/web/inc/functions.mailbox.inc.php
@@ -402,6 +402,13 @@ function mailbox($_action, $_type, $_data = null, $attr = null) {
             );
             return false;
           }
+          if ($domain == $MAILCOW_HOSTNAME) {
+            $_SESSION['return'] = array(
+              'type' => 'danger',
+              'msg' => sprintf($lang['danger']['domain_matches_hostname'], htmlspecialchars($domain))
+            );
+            return false;
+          }
           try {
             $stmt = $pdo->prepare("INSERT INTO `domain` (`domain`, `description`, `aliases`, `mailboxes`, `maxquota`, `quota`, `backupmx`, `active`, `relay_all_recipients`)
               VALUES (:domain, :description, :aliases, :mailboxes, :maxquota, :quota, :backupmx, :active, :relay_all_recipients)");
diff --git a/data/web/lang/lang.de.php b/data/web/lang/lang.de.php
index f71a653b..2f508e53 100644
--- a/data/web/lang/lang.de.php
+++ b/data/web/lang/lang.de.php
@@ -296,6 +296,7 @@ $lang['edit']['delete2duplicates'] = 'Lösche Duplikate im Ziel';
 $lang['edit']['delete1'] = 'Lösche Nachricht nach Übertragung vom Quell-Server';
 $lang['edit']['delete2'] = 'Lösche Nachrichten von Ziel-Server, die nicht auf Quell-Server vorhanden sind';
 
+$lang['add']['domain_matches_hostname'] = 'Domain %s darf nicht dem Hostnamen entsprechen';
 $lang['add']['domain'] = 'Domain';
 $lang['add']['active'] = 'Aktiv';
 $lang['add']['multiple_bookings'] = 'Mehrfaches Buchen möglich';
diff --git a/data/web/lang/lang.en.php b/data/web/lang/lang.en.php
index e3ed0d8b..6a0d7419 100644
--- a/data/web/lang/lang.en.php
+++ b/data/web/lang/lang.en.php
@@ -300,6 +300,7 @@ $lang['edit']['delete2duplicates'] = 'Delete duplicates on destination';
 $lang['edit']['delete1'] = 'Delete from source when completed';
 $lang['edit']['delete2'] = 'Delete messages on destination that are not on source';
 
+$lang['add']['domain_matches_hostname'] = 'Domain %s matches hostname';
 $lang['add']['domain'] = 'Domain';
 $lang['add']['active'] = 'Active';
 $lang['add']['multiple_bookings'] = 'Multiple bookings';