Single email Stuck in Backend Exchange Queue

Solution 1:

For more information, you can go into ESM and look at the queue. From the wording of your question, it sounds like you're already there. When you click on the name of the queue (name of the domain the mail is to be routed to), in the bottom pane there is a little box "Additional Queue Information" where you can get more info on why it's stuck in that queue. A quick google search after that might yield results.

EDIT: Based on your comments, I would look at this.

EDIT: For further troubleshooting, here are some links I would look at

Turning on Diagnostic Logging for Exchange 2003 <-- generates more info in Application Log in Eventvwr

How to use Queue Viewer to troubleshoot mail flow issues in Exchange Server 2003

Technet article regarding Event ID 4007 source MSExchangeTransport (good links here)

XFOR: Telnet to Port 25 to Test SMTP Communication <--I would try this first for any mail stuck in the queue issue first.

I just had to troubleshoot a mail queue problem in my own environment, and it turns out we don't have our PTR record set up for Reverse DNS 0_o

Solution 2:

If unfreeze didn't work did you try to force?

Try this:

Open Exchange System Manager: First Administrative Group > Servers> "Server Name" > Queues

Right click the queue in question and click Force Connection.

It could fail for a few reason Message size to large recipient doesn't exist or is unreachable domain does not exists or is unreachable etc...

You can click find messages and search for it. If there is only one that will make it easy. Check out the properties see if that sheds some light on it.