Apple Users

I did add my @att address to the Mail mailbox, and it worked sending and receiving, as well as from my start page through Yahoo. But my .mac address would only send out, & would never receive, once I signed up with att. Curiously, and more mysteriously, now, I am out of att, and on a different provider for all mail, BUT, I still can receive & send mail to my att. address through "Mail". I thought it would have stopped immediately when I stopped Uverse. Color me confused. I thought perhaps it was still working because I also have an IPhone served by ATT, which also sends, & receives, through all mailboxes entered into my phone settings, EXCEPT, mac.com.