How to logout/logoff from the email account ?

but what if i want to sign in with another email address on the same device? how do i log out of my email?

You can always enable a complex passcode if you do not like the simpler 4-digit one. You can also set the device to wipe itself of all data after 10 failed passcode attempts.

This is simple:

Go to settings and scroll down to mail.

Then click delete account

Sign in woth the new account you want to start using