How to log out of mail

The Mail app doesn't really have the concept of logging in and out - you can only remove your account's password from Settings > Mail, Contacts, Calendars, but that will only stop it downloading any new email, any email that has already been downloaded will be accessible within the app. If you want your email on the iPad to require a password to access it then you could either have a look in the store for a third-party email app, or just access your email via Safari (you can create a homescreen shortcut for your account's login page).

You can remove your account from your iPhone . In latest version go to settings the account the choose the account and select delete. It will be removed otherwise you can deselect the mail acces to your account.

You can't, using the built in mail program. Since the pad is designed as a single user device, once you get past the main passcode, the functions are open.

If you have an e mail account that you do not want others to see when they are playing around with your pad, simply turn the account off in settings, or delete it entirely, and access it using web mail.

(hoping for a change to this with a future iOS update, but you never know)