I’ve been watching for about 18 hours, and I think my email is fixed. Who messed it up? I believe I did, in the middle of resolving another problem, by unwittingly pressing a button that deleted my MX settings in Dreamhost that tell Fastmail it’s my email provider. Dreamhost Support tried to suggest this was the problem, but (not too surprisingly) I didn’t receive the message. I found their support message in their reporting system when I logged in to report another small problem unrelated to email.
The interesting part about a problem like this is that the email just vanishes. It doesn’t bounce, it doesn’t arrive, it’s not sitting in a spam filter. Email becomes unmail.
All those correspondences, neither here nor there; trees falling in a forest, a trumpet player in the attic, the disappeared.