Unless you have an unlimited data plan, you probably know how the importance closing down bandwidth hungry apps to avoid excessive charges. Receiving email on your iPhone doesn't consume a huge amount of bandwidth, but the little it does use adds up over time. Consequently, if you don't want to receive messages on your iPhone for a while, you'll need to sign out of your email account. However, an iPhone doesn't allow you to just log out of your email account like you would from a computer. Instead, you must turn off the iPhone's Mail function temporarily.
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Tap the "Settings" icon on the iPhone's home screen, followed by the "Mail, Contacts, Calendars" option.
Tap the email account that you want to log out of beneath the "Accounts" heading.
Slide the "Mail" option to the "Off" position. You will now be logged out of that email address on the iPhone until you turn the account "On" again.