Can´t receive Mails in trunk #639 ?!

[BeNe]

Yeah i typed the FQDN during the Setup.
ispCP put it in the main.cf - everything was right.

BUT - in my opinion is the "mail." before the hostname missing.
After the change from:

Code:

mydomain.tld

to

Code:

mail.mydomain.tld

Postfix delivers the mail now right and everything works.
There is a RFC (cant find it now) about the hostname for a Mailserver,
and this should always be "mail.hostname.tld".

Or i´m wrong ?