> I have gateway for incoming mail with postfix and ms exchange as final
> destination and outgoing smtp server.
> Exchange server are running with FQDN relay.domain.tld. This name is in
> the DNS as a single mx record of our zone.
> Can I set "myhostname" parameter with the same FQDN so as do not get
> mail loop errors.
The Postfix SMTP CLIENT will not DELIVER mail to remote SMTP SERVERS
that announce the same MTA hostname in the SMTP handshake.
You can tweak -o options in master.cf but this removes an important
safety mechanism against mail server meltdown.