The gods were not content to give us only one issue today from an external provider, but two!

At approximately 7pm the network that includes our mail server was on got hit by a massive denial of service attack.
The nice people at Shanghai Telecom decided that they would simply shut off routing for the entire subnet as their optimal solution.

We have a nice graph of that happening here:

Note the sudden precipitous drop in network traffic starting at approximately 7pm, which lasted until approximately 8pm.

We also have images of the DoS attack [although not completely, as our network was null routed (shut off) for the brunt of the attack]

You can see the sudden increase in incoming traffic in this image below (which occurred before they killed the network completely).
The green line which indicates incoming packets suddenly goes sky high before the network people shut off the network.

Some of the other servers also got hit by this – notable our web servers, although they didn’t cut those off thankfully.
See below for a view of that traffic.

As the old curse goes – may you live in interesting times.
Some days are more interesting than others!