The SMTP connector should not crash because of an influx of messages detected in the queue. The agent is detecting a spike in volume in the outbound queue. You need to inspect the SMTP log files to determine why and who is relaying the messages. Sounds like a spammer a guessed a password and is relaying spam. For the SMTP crash is the service actually crashing you need to start it again or is it that its not processing messages but the service is running?
It was a user who auto forwards emails from a particular address which is rather frequent.
I have installed service protector which will restart the service if it stops.