The cPanel doesn't really do an accurate job of detecting when user services and not responding. When this issue first came in, I had one of the server techs restart exim, as this was the process that was flagged as failed. It was running fine before the restart and restarted without issue. Also, the load detector is really inaccurate. It shows the load somewhere around what it actually is, but it does not take into account there are 4 CPU's instead of just one.
Now for the cause of the outtage. There was a cronjob on the server that got stuck in an infinite loop. It has been disabled and the originating user has been notified. This is something that can always happen in a shared server environment. To my knowledge (I worked the night shift last evening) email would have only been effected for a couple of hours, possibly around 6. Issues like this always take a little longer than normal to find as the cause isn't directly apparent. I apologize that this happened and the inconvenience that it has caused you and since the offending cron job has been disabled, it should not recur.