OK, I got so far that I can send/receive mail localy and I can send mail to other domains (gmail for example). BUT I can not receive mail from any other domain. The message I get when trying to send mail from a gmail account to my server is:

Technical details of permanent failure:
PERM_FAILURE: Google tried to deliver your message, but it was rejected by the recipient domain.
We recommend contacting the other email provider for further information about the cause of this error.
The error that the other server returned was: 554 554 5.7.1 <e-mail address>: Relay access denied (state 14).