Ah.

So, Dreamhost's mail is down. Never thought I'd say, "Luckily, I still have Yahoo," but there you go.

From Dreamhost's support system:

"A spammer initiated a massive attack on a domain serviced by the "cluster"
of mail servers that hosts at least one of your domains' mail. We've
blocked the spammer and are clearing out the tens of thousands of messages
left by the attack. It's made mail slow on this group of machines, and has
exacerbated the high load our mail servers are already experiencing due to
MyDoom, the latest Windows virus. All mail will be delivered, just slowly.
We're working to ensure that a similar attack won't slow mail down so
badly in the future."