And the problem is back again, this time on another domain and with extra complications.
When you send a message to this domain postfix wil return this:
Final-Recipient: rfc822; firstname.lastname@example.org
Original-Recipient: rfc822; email@example.com
Diagnostic-Code: X-Postfix; maildir delivery failed: create
* another question on the side, the hostname for this server during install was ds2.adsl.utwente.nl but that was temporary, postfix/spamassassin still use this but I can't find it in the config files. Where should I look to change this?