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Error: #550 4.4.7 QUEUE.Expired; message expired ##

I am having an issue with one of my client’s exchange servers. They have one external client that they cannot send any email to but if I get the external client to send a test message, it will be received without any issues. I have confirmed that he is using the same email address as we have. The domain is @iastate.edu

When I send a test message to the external clients email address, it shows up in the outbound exchange queue and never leaves. Eventually, I get the following error;
Error: #550 4.4.7 QUEUE.Expired; message expired ##
If I open the receive log files, I can see that there are no messages showing an attempt to deliver that message.
The folder I was looking in was as follows;
C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\Logs\ProtocolLog\SmtpSend

Exchange mail flow troubleshooter doesn’t show anything wrong

What can I do to narrow down where the problem may be?

ASKER CERTIFIED SOLUTION

Andy M

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johnny181

ASKER

Ah, that is the funny thing. I went to MX Toolbox and their mail server shows mailin.iastate.edu. When I ping that from the server, I get a response of 129.186.140.10.

Andy M

That appears to be correct - that hostname resolves to that IP on my system as well. If you are getting a ping response on your mail server for that then the connection/dns seems fine. I would try sending an email via telnet through that - may give you an idea of what part the process fails.

johnny181

ASKER

Over the weekend, I went through the DNS on the Windows 2008 server and all appears to be good.
I sent another test a few minutes ago and one thing that I see now in the SMTP log files is the following;
451 4.7.1 Please try again later (TEMPFAIL)