I am getting random "new mail" notifications with both MailFu and SLMail (which would also show the mail icon on the minimap). It has been happening for about a week now. Not even when touching a mailbox - sometimes I notice it when I'm in an instance, or porting. I haven't caught when it happens.
One time it is definitely happening is when someone sends me a mail. Yes, even thoguh it won't arrive for an hour, somehow MailFu knows and declares that I have new mail. I've tested this with friends on Vent and while it doesn't happen every time it is reproducable. It's definitely not a coincidence.
At a guess there is something up with the Blizzard events since there's no way MailFu would know otherwise?
I'm also getting the new mail alert when opening a blank inbox as someone else mentioned, happens 30-50% of the time I guess.