Exchange 5.5 rejection message

I preiodically see the following error message from the MTA and I have not found the root cause of the problem. I find references to similiar issues in TechNet and I have spoken with MS Support, but they reference TechNet.

Any ideas???

Your message did not reach some or all of the intended recipients.

Subject: Accepted: Updated: 349013 HV Degas Ckt
Sent: 10/22/02 11:30 AM

The following recipient(s) could not be reached:

ntuser on 10/22/02 11:27 AM The recipient name is not recognized
The MTS-ID of the original message is: c=US;a= ;p=CTI;l=GP1-021022153008Z-41695
MSEXCH:MSExchangeMTA:BOULDER:GP1