Merge #1901

1901: treat localpart case insensitive again r=mergify[bot] a=ghostwheel42

## What type of PR?

bug-fix

## What does this PR do?

fixes error introduced by #1604 where the localpart of an email address was handled case sensitive.
this screwed things up at various other places.
 
### Related issue(s)

closes #1895
closes #1900

Co-authored-by: Alexander Graf <ghostwheel42@users.noreply.github.com>

core/admin/mailu/models.py

@@ -57,10 +57,9 @@ class IdnaEmail(db.TypeDecorator):
 
     def process_bind_param(self, value, dialect):
         """ encode unicode domain part of email address to punycode """
-        localpart, domain_name = value.rsplit('@', 1)
+        localpart, domain_name = value.lower().rsplit('@', 1)
         if '@' in localpart:
             raise ValueError('email local part must not contain "@"')
-        domain_name = domain_name.lower()
         return f'{localpart}@{idna.encode(domain_name).decode("ascii")}'
 
     def process_result_value(self, value, dialect):
@@ -277,6 +276,7 @@ class Domain(Base):
 
     def has_email(self, localpart):
         """ checks if localpart is configured for domain """
+        localpart = localpart.lower()
         for email in chain(self.users, self.aliases):
             if email.localpart == localpart:
                 return True
@@ -355,8 +355,8 @@ class Email(object):
     @email.setter
     def email(self, value):
         """ setter for email - sets _email, localpart and domain_name at once """
-        self.localpart, self.domain_name = value.rsplit('@', 1)
+        self._email = value.lower()
-        self._email = value
+        self.localpart, self.domain_name = self._email.rsplit('@', 1)
 
     @staticmethod
     def _update_localpart(target, value, *_):
@@ -389,8 +389,7 @@ class Email(object):
     def resolve_domain(cls, email):
         """ resolves domain alternative to real domain """
         localpart, domain_name = email.rsplit('@', 1) if '@' in email else (None, email)
-        alternative = Alternative.query.get(domain_name)
+        if alternative := Alternative.query.get(domain_name):
-        if alternative:
             domain_name = alternative.domain_name
         return (localpart, domain_name)
 
@@ -401,12 +400,14 @@ class Email(object):
         localpart_stripped = None
         stripped_alias = None
 
-        if os.environ.get('RECIPIENT_DELIMITER') in localpart:
+        delim = os.environ.get('RECIPIENT_DELIMITER')
-            localpart_stripped = localpart.rsplit(os.environ.get('RECIPIENT_DELIMITER'), 1)[0]
+        if delim in localpart:
+            localpart_stripped = localpart.rsplit(delim, 1)[0]
 
         user = User.query.get(f'{localpart}@{domain_name}')
         if not user and localpart_stripped:
             user = User.query.get(f'{localpart_stripped}@{domain_name}')
+
         if user:
             email = f'{localpart}@{domain_name}'
 
@@ -416,15 +417,15 @@ class Email(object):
                     destination.append(email)
             else:
                 destination = [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
 
-        if stripped_alias:
+        if stripped_alias := Alias.resolve(localpart_stripped, domain_name):
             return stripped_alias.destination
 
         if pure_alias: