Okay, I spent a couple of hours trying to get Thunderbird.  I downloaded it and got the set-up started.  But somehow, it got hold of the info for the very old AT&T account.  I've been going through, trying to delete all references to prior accounts, but it hasn't worked, so far.  
It would be easier if I knew how computers 'think', but for me, it's on the same level as flying by flapping my arms.
Sue