Resolving email delayed problems in Exchange 2007

After the troubleshooting I've done so far, I'm thinking this might be related to DNS records. The problem I'm trying to resolve is that employees at (let's call them the acme.com domain) get a delayed status notification from their Exchange server when sending emails to someone at the me.com domain. Here is the Exchange message:

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Reporting-MTA: dns; acmeex.acmeex.com Final-recipient: RFC822; user1@me.com Action: delayed Status: 5.4.0 X-Supplementary-Info: < #4.4.7 smtp;400 4.4.7 Message delayed> X-Display-Name: Taylor Smith
********************

So far Exchange Message Tracking has lead me to no better identifiable errors to resolve. Blacklists look clean. It's only delaying sending to this Apple me.com domain.

Thanks for any helpful input.
matrixcomputerAsked:
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TrackhappyConnect With a Mentor Commented:
Check that you have a reverse dns entry setup correctly for your domain. They might be greylisting you if they cannot verfiy your mx record against your domain name.
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vanbarsounCommented:
Most likely it's an issue at the remote end. Try sending using a different email domain account and see if you get the same result.
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matrixcomputerAuthor Commented:
Both good points. Thanks.

1) Days ago I opened a case with Apple and have been in direct contact with an Apple technician who was assigned to this case. We've been testing with multiple email accounts sending to the me.com, apple.com, and mac.com domains with inconsistent results so far. But Apple did say they tracked inbound test messages and did not see any filtering happening to them, and we've confirmed that some emails are received just fine.

2) DNS could be the problem; I am just hesitant to blame DNS because of the limited scope of the problem, which seemed to have started around Sept. 1 as best I can determine so far. Their internal Exchange server's local Windows domain is acmeex.com, not acmeex.local, and the email domain Exchange is moving mail for is acme.com. The Internet doesn't even know the domain acmeeex.com exists so reverse or any lookups fail for that domain.

The 5.4.0 error they get indicates potential DNS problems. Next, I'm going to clean up their DNS as much as I can.
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matrixcomputerAuthor Commented:
One of the things I looked at as something to be tried is to change the External DNS Lookup setting on the Transport Hub from using the internal NIC settings to using external DNS servers but I had not tried changing it yet. I just came across this solution:

http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/Q_24500335.html

I just made that change and am re-testing now.
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Stephan BourgeoisIT SpecialistCommented:
We're having problems with me.com as well: it appears to be related to DNS.
The MX query result is large enough that it has to be retried with TCP vs the usual UDP.
If you have a firewall, is port 53 TCP outbound open for your server?

As an aside, other people are having issues with me.com:
http://discussions.apple.com/thread.jspa?messageID=12625624&tstart=0
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