I have an Exchange 2003 server I take care of with an occasional problem. One user sending meeting cancellations and possibly meeting requests to multiple external users at multiple domains has the message become stuck in the queue for the outbound connector. I don't know if this happens with all her meeting cancellations sent to external users but it is at least some. It may also happen with meeting requests but I can't, at this point, be sure. Here's what I know:
1) It's only this one user who experiences the issue.
2) The queue for the "Default Outbound" SMTP connector goes into retry and other messages appear to be stuck behind this one.
3) The message causing the issue usually - maybe always - has multiple external recipients.
4) It today's case, the message is large-ish (22,529). I'm not sure if that's always the case.
5) Looking at message tracking, the last entry shows "SMTP: Message Routed and Queued for Remote Delivery"
6) There is nothing in the SMTP logs related to this message. This indicates to me that it is not getting as far as a delivery attempt by the SMTP service to any remote server.