Problem with sending mails from ISPC3 server

[manarak]

I run a server with Debian 5, ISPC3 and Postfix.

I have an OSCommerce installation that sends emails either by mail() or sendmail (it doesn't matter how).

The mail gets rejected by the mailservice gmx.net

here is the log:
Aug 16 13:21:59 server2 postfix/smtp[13640]: A28214E805F: to=, relay=mx0.gmx.net[213.165.64.100]:25, delay=0.32, delays=0.01/0.01/0.11/0.2, dsn=5.1.8, status=bounced (host mx0.gmx.net[213.165.64.100] said: 550 5.1.8 Cannot resolve your domain {mx056} (in reply to MAIL FROM command))

who can please help me diagnose this problem?

[till]

Looks as if you dont have a fully qualified domain name in your postfix configuration. Check postfix main.cf and /etc/mailname that they contain a fqdn for example mail.yourserver.com and not just mx056

[manarak]

thank you - I rummaged everywhere on the server and saw a faulty MX entry in the DNS.
Somehow it had two trailing points instead of one.
Inexplicably, the domain was working fine inspite of faulty DNS entries.