--@mac.com address just came back!!

Long ago I had a --@mac.com email address, and that is what I have always kept as an AppleID. However, I eventually stopped paying for one of the versions of their online services, and lost my mac.com email address. With the transition to the free services, I got an icloud.com and me.com address, but the mac.com address never came back.

Now, lo and behold, I got an email to that address from a company I used to deal with. I sent one to the same mac.com address, and it went through and I received it! Which is puzzling because I don't have that account in Mail, nor do I have it listed as an alias for any account.

Did apple change something? Now that I am receiving emails at that address, how could I send them?