I added my email address to a yahoo group, but it still doesn't recognize it. Is the real email address that's sent to yahoo something different?

no, that is as much an email addres as anything there is.

My recommendation? Remove it immediately. If it starts getting spammed you are stuck with. Don't post the addresses places, etc., you can't change it until you change carriers, and that might happen in a year or three and who is going to remember where all they subscribed with that address. Get a gmail or something.