Hello,
I have a mailcow instance running, which is serving mails for several domains. Everything works fine except one thing:
One domain is not served primary by this mailcow instance. Instead a different provider serves the domain and forwards mails for some addresses to mailcow.
MX-Record for example.com points to some-cloud-service.
MX-Record for example2.com points to mailclow.
mailcow has both domains configured: example.com and example2.com
There is a mailbox foo@example.com with an alias for foo@example2.com.
In some-cloud-service there is a address foo@example.com, which forwards all mails to foo@example2.com.
In some-cloud-service there are also normal mailboxes like bar@example.com, which are unknown to mailcow.
When the mailbox bar@example.com tries to send an email to foo@exapmle.com, the mailbox bar@example.com gets an undeliverable notification:
The following address failed:
foo@example.com:
SMTP error from remote server ... reason: 550 5.1.0 <bar@example.com>: Sender address rejected: User unknown in virtual mailbox table
Any ideas how to solve this?