I haven't seen any change on login, that is, MailFu still displays that you've got mail if you have it (green icon, 0 count, presumably because it doesn't know how many are in there, just that you have mail).
What's changed is mail notification while in game. I'll get the chat spam that an auction has expired, been won, sold, etc. but MailFu does nothing. Doesn't turn green, red, display a number, a tooltip, anything. I'd venture to say that friend emails won't display a notification while in game either.
I'm having this problem too. Tried reverting to a version I know works, but I've just converted to external libraries so I'm not sure I copied everything correctly -or- it may be a library issue. I'm concerned that this isn't being looked at anymore because Tekkub, the listed author, is no longer contributing to this site, from what I understand.