I recently had to help a customer clean up their SBS 2003 server which had been used to send out spam. It seems that one of their user accounts had been compromised, and we were able to stop the spam by changing the user’s password. The server’s performance was horrible, even after a reboot, and we found messages stuck in over 500 SMTP queues. Rather than clear the queues one at a time, I used the Aqadmcli tool to delete all the stuck messages at once.
To clear all the SMTP queues at once, run the following from a command prompt on the Exchange server:
where [servername] is the name of the Exchange server containing the queues you want to clear.
You can also delete messages from a particular sender using the syntax
You can read more about this tool here [via the Wayback Machine]