I got this thing described here as a mail yesterday: Help:Login_notifications#Successful_logins
I may have logged in yesterday, that may be correct. However, I am not aware that I have ever opted-in/enabled that feature… (I also did not got it from any other wiki yet.)
Maybe this was a false-positive. I do not even know, where I could enable/disable that feature (although you possibly could document that here). And after logging in again now for posting this, I also did not get any mail.