I sent a test e-mail to a zimbra mail account from outlook express.
An e-mail was returned from the Mail Deliver System with the following content;
This is the Postfix program at host mailhost.bhburgis.com.
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 Postfix program
<email@example.com>: Host or domain name not found. Name service
error for name=mailhost.bhburgis.com type=A: Host not found
Below is the information that was contained in the delivery report.dat
Reporting-MTA: dns; mailhost.bhburgis.com
X-Postfix-Sender: rfc822; firstname.lastname@example.org
Arrival-Date: Mon, 7 Nov 2005 03:34:33 -0500 (EST)
Final-Recipient: rfc822; email@example.com
Diagnostic-Code: X-Postfix; Host or domain name not found. Name service error
for name=mailhost.bhburgis.com type=A: Host not found