I’ve had several incidents where mail was stuck in the categorizer. Mail was sent internally and externally. I checked the Message Tracking Center and the following was showing on the messages in question:
SMTP: Message Submitted to Advanced Queuing
SMTP: Started Message Submission to Advanced Queue
SMTP: Message Submitted to Categorizer
When I first noticed this happening I saw an error in the application log that repeated every minute from the MSExchangeAL event ID 8331. I restarted the Exchange System Attendant service and this error disappeared. However, I’m still having the problem with some messages not reaching their destination. So, I don’t know if it was related. This is a major production server so I haven’t completely rebooted it. Any help would be GREATLY appreciated.