I didn't see the letter until I got home at 6:30 and the office was closed. So now I'll be up all night (luckily, that's pretty much my schedule anyway) until I can go there in person in the morning.
The guy at the desk knew nothing about this but thinks it's probably no cause for worry (maybe a buyout offer; I'm renting since 1975 and the building went condo in the early '90s). I'm thinking the worst, that I'll lose my apartment (Too cluttered! OUT! Your neighbor hears you typing clickety-clackety all night. OUT! Is that piano playing or did you have a stroke? OUT! The stuffed lambs are baaing. OUT!).
There's a mailing list for my complex but they had problems with AOL kicking out mail as spam so AOLers have to forward items to the list moderator and wait for her to forward things back. I sent an inquiry to see if this is a mass mailing or just me, but it may not get through channels in time. (And yes, I have an almost-never-used MSN address but I didn't join the list with it. A client pays for my AOL account.)
Let's hope it's nothing.