Problems sending Mails

Hello Community

I setup my Mac OS X 10.8 Mail Server successfully (thanks to Mike23 for yor help). Now I configrued Mail and Web addresses and all seems to work very well. Now, sometimes, I receive a Mail Delivery System error from some receipients. Here is a copy of the error message:

This is the mail system at host server.domain.tld.

I'm sorry to have to inform you that your message could not

be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can

delete your own text from the attached returned message.

The mail system

<fk@xyz.net>: host mail.xyz.net[78.xx.xx.184] said: 554

5.7.1 Client host rejected: cannot find your reverse hostname,

[80.xx.xx.206] (in reply to RCPT TO command)

Reporting-MTA: dns; server.domain.tld

X-Postfix-Queue-ID: 870C512C115

X-Postfix-Sender: rfc822; dominique@domain.tld

Arrival-Date: Thu, 4 Oct 2012 09:24:32 +0200 (CEST)

Final-Recipient: rfc822; fk@xyz.net

Original-Recipient: rfc822;fk@xyz.net

Action: failed

Status: 5.7.1

Remote-MTA: dns; mail.xyz.net

Diagnostic-Code: smtp; 554 5.7.1 Client host rejected: cannot find your reverse

hostname, [80.xx.xx.206]

I configured DNS on my MAC Server with my Domain as follows:

Server Name: server.domain.tld

DNS:

Primary Zone:

domain.tld - Machine

server.domain.tld - Alias

mail.domain.tld - Mail Exchanger

mail.domain.tld - Alias

Reverse Zone:

206.xx.xx.80.in-addr.arpa:

server.domain.tld

mail.domain.tld

So I think that the DNS system should be not the problem ... 😟

Any Tips please?

Thanks

Dominique