I've installed dovecot, postfix and roundcube on an ubuntu 12.04 box. The system is basically working - i.e it is able to send/receive mails to/from other domains.
However, some domains cause the following error message in /var/log/mail.log
Jul 15 01:59:21 one postfix/smtp: 0D0399C025F: to=<email@example.com>, relay=sm01.destdomain.com[x.x.x.x]:25, delay=0.56, delays=0.4/0/0.06/0.1, dsn=5.5.2, status=bounced (host sm01.destdomain.com[x.x.x.x] said: 504 5.5.2 <contact@localhost>: Sender address rejected: need fully-qualified address (in reply to RCPT TO command))
Do you have any idea what's wrong here? I.e. How to force postfix to use "firstname.lastname@example.org" instead of "contact@localhost" when connecting to another mail server?
Any hints are appreciated.