Reverse the resolution order of user and alias

Since it’s common for wildcard~ish systems to prefer concrete objects over
wildcards, and aliases can be broad-wildcards (think catchall, %@xxx.tld), it
may be more intuitive for users that user-names rank higher than aliases. This
makes it impossible for user-names to be unreachable, since they can be
completely overridden by a catchall otherwise.

This changes default behavior, and is not configurable.

closes #815

core/admin/mailu/models.py

@@ -266,16 +266,6 @@ class Email(object):
         if os.environ.get('RECIPIENT_DELIMITER') in localpart:
             localpart_stripped = localpart.rsplit(os.environ.get('RECIPIENT_DELIMITER'), 1)[0]
 
-        pure_alias = Alias.resolve(localpart, domain_name)
-        stripped_alias = Alias.resolve(localpart_stripped, domain_name)
-
-        if pure_alias and not pure_alias.wildcard:
-            return pure_alias.destination
-        elif stripped_alias:
-            return stripped_alias.destination
-        elif pure_alias:
-            return pure_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))
@@ -288,6 +278,16 @@ class Email(object):
                 destination = [user.email]
             return destination
 
+        pure_alias = Alias.resolve(localpart, domain_name)
+        stripped_alias = Alias.resolve(localpart_stripped, domain_name)
+
+        if pure_alias and not pure_alias.wildcard:
+            return pure_alias.destination
+        elif stripped_alias:
+            return stripped_alias.destination
+        elif pure_alias:
+            return pure_alias.destination
+
     def __str__(self):
         return self.email