This is not a question - more a comment and explanation for future reference, in case someone with the same problem searches these forums for an answer.
I followed the Virtual Users And Domains With Postfix, Courier And MySQL (+ SMTP-AUTH, Quota, SpamAssassin, ClamAV) HowTo (see http://www.howtoforge.com/virtual_po..._quota_courier
). Everything worked fine except for mail delivery to virtual accounts. I had the following error in my log files:
Nov 2 17:21:10 server postfix/local: A7E502342AF: to=<email@example.com>, relay=local, delay=0.02, delays=0.01/0/0/0.01, dsn=5.1.1, status=bounced (unknown user: "inquiry")
My problem was that in my /etc/postfix/main.cf file, I had the following
mydestination = mail.mydomain.com, mydomain.com, localhost, localhost.localdomain
Where mydomain.com (not my real domain...) is my main domain name and mail.mydomain.com the FQDN of the server. To fix the issue, I had to remove mydomain.com from the main.cf mydestination directive and put it into the domains table of the MySQL database. After that everything was working flawlessly.
Thanks Falko for this great HowTo!