421 Service Temporarily Unavailable

Hello Experts

I'm working on trouble tickets in my company and ran across one that I'm not sure about solving.  My user didn't tell me which mail program was used, so I listed them both.  I know my company sends out large amounts of email through PowerMTA and I thought maybe we were blacklisted or something, but can't find anything that would support that idea.

So, what do you guys think?  Is this something on my server end or the receiving end?  My diagnostic info is.....

Your message has encountered delivery problems
to the following recipient(s):
Delivery failed
421 Service Temporarily Unavailable
No recipients were successfully delivered to.
Reporting-MTA: smtp.domain.com
Received-From-MTA: dns; domain.com (unverified [x.x.x.x])
Arrival-Date: Fri, 25 Mar 2011 14:56:35 -0400

Final-Recipient: rfc822; email@domain.com
Action: failed
Status: 5.4.7 (Permanent failure - routing/network: delivery time
Remote-MTA: dns; cluster4a.us.messagelabs.com (is this some spam agency's dns?)
Diagnostic-Code: smtp; 421 Service Temporarily Unavailable

Any help would be greatly appreciated.

Ray DrummondLan Administrator IIIAsked:
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