Email is (was) broken!!!
Yes, Sunday morning, at around 05:23 the mail server power backup failed. Yes, second one in 2 weeks.
So, when it was brought to my attention around noon (sorry!!!) I ran down to the office and started repairs. These servers aren't very happy if the power fails, and recovery can take a while, but its moving forward now.
I have added additional notification methods to my "is it broken" system, next time this happens (It better not!!!) things will be caught much sooner.
(4:08 pm the last of the mail has cycled through, all services are back to normal)