Some while back, Google changed all the user's email addresses to something like
firstname.lastname@example.org (before that, for some users, it was
email@example.com). I can still receive messages to the
@googlemail address, but cannot send ones.
This usually would not be a problem but I am kind of stuck on a mailing list and cannot unsubscribe, because the bot that manages the list does not recognize my
@gmail address. Of course, I could contact the admin and let him remove me manually, but I would rather find out how to do it without bothering him.