I was having problems with one of my accounts in Mail, so did what I have done before - deleted and re-installed. Except that Mail says that account already exists and will not allow me to install it.I have looked through all the postings in MS forums related to this topic and found some good comments and suggestions. I tried the Powershell scripts to uninstall Mail, which worked (after a very long time), then re-installed Mail. It immediately recognised my Gmail account, which surprised me, as I expected to have to re-enter each of my accounts. When I added my other account, it came back with the very same message "Account already exists".