diff --git a/core/admin/mailu/configuration.py b/core/admin/mailu/configuration.py
index 8d4d334a..1f2a9239 100644
--- a/core/admin/mailu/configuration.py
+++ b/core/admin/mailu/configuration.py
@@ -49,7 +49,7 @@ DEFAULT_CONFIG = {
     'DKIM_PATH': '/dkim/{domain}.{selector}.key',
     'DEFAULT_QUOTA': 1000000000,
     'MESSAGE_RATELIMIT': '200/day',
-    'RECIPIENT_DELIMITER': None,
+    'RECIPIENT_DELIMITER': '',
     # Web settings
     'SITENAME': 'Mailu',
     'WEBSITE': 'https://mailu.io',
diff --git a/core/admin/mailu/internal/views/postfix.py b/core/admin/mailu/internal/views/postfix.py
index 44a685c9..ab965967 100644
--- a/core/admin/mailu/internal/views/postfix.py
+++ b/core/admin/mailu/internal/views/postfix.py
@@ -140,8 +140,7 @@ def postfix_sender_login(sender):
     localpart, domain_name = models.Email.resolve_domain(sender)
     if localpart is None:
         return flask.jsonify(",".join(wildcard_senders)) if wildcard_senders else flask.abort(404)
-    if delim := flask.current_app.config.get('RECIPIENT_DELIMITER'):
-        localpart = localpart.split(delim, 1)[0]
+    localpart = localpart[:next((i for i, ch in enumerate(localpart) if ch in flask.current_app.config.get('RECIPIENT_DELIMITER')), None)]
     destination = models.Email.resolve_destination(localpart, domain_name, True)
     destination = [*destination, *wildcard_senders] if destination else [*wildcard_senders]
     return flask.jsonify(",".join(destination)) if destination else flask.abort(404)