I just received a server report: SMTP Server Remote Queue Length Alert .
Indeed there are several messages - some many days old - in Exchange/Servers/Queues.
Searching produced an MS KB message ( http://support.microsoft.com/?kbid=835734
I installed this fix, but it still leaves several questions:
1. This fix is from 2004. I use SBS R2. I would expect this fix to be included. Maybe I have an other problem?
2. The messages are still in the queue after the fix. Should I remove them manually?
3. Have they been sent at all? I do not receive complaints of double sent messages.