Attempt stripping recipient delimiter from localpart

Since postfix now asks us for the complete email over podop, which
includes the recipient-delimiter-and-what-follows not stripped, we need
to attempt to find both the verbatim localpart, as well as the localpart
stripped of the delimited part ….

Fixes #755

core/admin/mailu/models.py

@@ -260,10 +260,19 @@ class Email(object):
 
     @classmethod
     def resolve_destination(cls, localpart, domain_name, ignore_forward_keep=False):
+        localpart_stripped = None
+        if os.environ.get('RECIPIENT_DELIMITER') in localpart:
+            localpart_stripped = localpart.rsplit(os.environ.get('RECIPIENT_DELIMITER'), 1)[0]
+
         alias = Alias.resolve(localpart, domain_name)
+        if not alias and localpart_stripped:
+            alias = Alias.resolve(localpart_stripped, domain_name)
         if alias:
             return alias.destination
+
         user = User.query.get('{}@{}'.format(localpart, domain_name))
+        if not user and localpart_stripped:
+            user = User.query.get('{}@{}'.format(localpart_stripped, domain_name))
         if user:
             if user.forward_enabled:
                 destination = user.forward_destination