my mistake ... i allways use the minimal install iso as i did with the postfix testing instalation
P.S. if your postfix server is on the same box as your MX record you should not add this in your database
INSERT INTO `transport` (`domain`, `transport`) VALUES ('example.com', 'smtp:mail.example.com');
it will create a loop and mail that your are sending to the localdomain (domain hosted on the box) won't be sent and as a result using mailx to send a wellcome message and create the maildir for the user will not work and you'll get an error on the webmail login
ERROR: Connection dropped by IMAP server.
Mar 20 09:11:54 server imapd: chdir example.lan/test/: No such file or directory
Mar 20 09:11:54 server imapd: firstname.lastname@example.org: No such file or directory