I was using my yahoo mail for my email on my iphone for a short time. I didn't like that it was always sitting there and I wasn't able to log out or lock it with a password. I kept messing with it and couldn't find the "log out" option. It was driving me crazy. All I could figure out how to do was to view all of my folders and reply or send new emails. I could also delete email but couldn't log out. I finally realized that it can't be done from the email app itself. You have to go into your settings and click on your email, then click on delete account.