I got on a mailing list for something from IBM. The unsubscribe link took me to a page that always said it was "temporarily" unavailable I should try again later. The first time I gave them the benefit of the doubt. After a few tries over the course of months, I decided that it was permanently unavailable, and if it really was broken, they didn't have any motivation to fix it. So I set up a filter to automatically delete everything from that domain.