Mail not working?

[joximu]

yes - use a hostname and not only a domain name.
e.g. you can use ispcp.yourdomain and for the panel: adminpanel.yourdomain

This should be better.

as a fast'n'dirty hack you can change the $myhostname in main.cf to something like http://www.frede92.lir.dk - this is not elegant but could work...