I've been blamed for ruining a marriage, I am innocent, what should I do?

The man is married and you need to let it drop. Why don't you know the wife's email address? Sounds like you are a little more involved than you care to admit because you don't seem to think of the wife and her feelings. He is trying to save his marriage and that comes first. No matter where the email came from, the friendship between you and a married man caused it to come from someone concerned for the wife.