Undelivered Mail - What could I have missed in configuration?

[AZMel]

I have 25 users setup and all work fine but my account keeps getting this e-mail about every 20 seconds or so. I am able to send and receive e-mails, this one just happens to keeps showing up in my inbox.

This is the Postfix program at host yyy.org.

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

<admispconfig@localhost.localdomain>: Host or domain name not found. Name
service error for name=localhost.localdomain type=A: Host not found



Reporting-MTA: dns; yyy.org
X-Postfix-Queue-ID: DB81D8605
X-Postfix-Sender: rfc822; xxx@yyyy.org
Arrival-Date: Wed, 10 Jan 2007 15:34:06 -0700 (MST)

Final-Recipient: rfc822; admispconfig@localhost.localdomain
Action: failed
Status: 5.0.0
Diagnostic-Code: X-Postfix; Host or domain name not found. Name service error
for name=localhost.localdomain type=A: Host not found

Thanks for your help,

Mel