Our "Premium Antispam" license from Symantec expired 2 days ago. I was concerned that the delay in getting a new license installed might cause issues, but was reassured that there was a full month's grace period. So I relaxed a bit.... wrong answer.
I now find myself in a high-tech skinner box. The spam filter turns itself off at Midnight each day now... and will resume functioning if I log into the server and re-enable it. I'm now doing battle with an evil cron job. I'm pissed.