I am running an Exchange 2k3 environment in a native Server 2k3 (all enterprise) environment. We have a Linux front end mail exchanger (MX) that sends incoming emails to the first Exchange mail server (MS1) that handles routing from there. The SMTP "Messages Pending Submission" queue on MS1 has been periodically building up usually just during the peak time of the day. Recently, it has become a major problem with it occurring during the night and in much greater numbers (60K emails). 70-80% of these (at least) are SPAM, and we have Exchange's intelligent message filter and GFI Mail Essentials running to help this situation. I don't believe that volume is the issue. I think it is a configuration problem. The default SMTP Virtual Server (VS) is in a constant retry state with the message at the bottom of the screen being "Unable to deliver the message because the destination address was misconfigured as a mail loop." We have looked at the associated KB article on MS's website, and we do not have 2 VS configured on the same machine as it suggests. I will be glad to offer any additional information needed. I greatly appreciate any help offered.