My version is Zimbra 7.2.0_GA_2669

I can send e-mail using Zimbra web mail to all domain, include, but when use a client, example Mozilla Thunderbird,
I get this error ( Undelivered Mail Returned to Sender ) .
But any other domain I can send mail, just can't send
mail to mydomain.comusing a client like Mozilla Thunderbird. What is the problem ?

Undelivered Mail Returned to Sender

This is the mail system at host machine1.local.

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


Reporting-MTA: dns; machine1.local
X-Postfix-Queue-ID: C6B1DCC025A
X-Postfix-Sender: rfc822;
Arrival-Date: Fri, 21 Dec 2012 10:57:18 -0200 (BRST)

Final-Recipient: rfc822;
Original-Recipient: rfc822;
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix;