We have a security block in place to shutoff an account if it sends an excess of 500 messages in under 10 minutes.
When this limit was hit we went in to spool management and deleted the remaining messages sending from the account. Doing this locked up the spool and would not let any other messages send.
We had to restart the service and also kill the stuck process to get this to clear up.
Wanted to report this and see if anyone else has experienced something similar.