Emailserver not sending mails to outside domains

Hello together,

after a summer break and some updates my beloved emailserver is telling me:

postfix/smtpd[10276]: NOQUEUE: reject: RCPT from unknown[]: 550 5.1.1 <>: Recipient address rejected: User unknown in virtual mailbox table; from=<> to=<> proto=ESMTP helo=<>

Is some able to point me in some direction?
The setup is an old howto: having ox_app_suite on another server than the univention-mail-app.
This was working for some years now. Anyway: the message is independent from the client I’m sending email with.

I see some changed files for the ldap connection in the postfix files on 9.8.23 - maybe related?

Internal emails are still delivered.


Maybe the mail domain of the recipient ( is configured as a local mail domain? We have notices some changes after updating from UCS 4.4 to 5.0.

Check udm mail/domain list if you are on UCS 5.0.

1 Like

:thinking: how did this entry get there? :grinning:

But it was, so thank you!

how did this entry get there?

Check the UCR variable ucsschool/import/generate/mail/domain. Probably it is set to yes.

If so: Whenever you create/import a user that has a primary mail address with an unknown domain part (e.g., then UCS will create a matching mail domain for you.

Ah, allright. I don’t have UCS at school installed, so the variable doesn’t exist.
But maybe there is another one. I will look into this.