In iOS 8.3, the option to remove an email account from your iPhone is not in the native Mail app, but through the Mail, Contacts, Calendars section of your iPhone's Settings menu. The deletion process only stops your iPhone from exchanging messages with your email account; it does not affect your account's original settings and options.
Open the Settings screen by clicking the Settings icon on your iPhone's Home screen.
If the Settings icon is not on the Home screen, use the Spotlight search feature to find the icon. Swipe down from the center of the Home screen and type Settings in the Spotlight search bar.
Scroll down the Settings screen and then select Mail, Contacts, Calendars to open the Mail, Contacts, Calendars screen.
Select the account you want to delete in the Accounts section of the screen.
In addition to the iCloud Settings screen, you can also sign out of your iCloud account through the Mail, Contacts, Calendars screen. Open the Mail, Contacts, Calendars screen, tap iCloud in the Accounts section, scroll down the screen and then tap Sign Out.
Tap Delete Account at the bottom of the screen.
Instead of deleting your email account, slide the account's Mail switch to the Off position to stop the Mail app from accessing your email messages.
Tap Delete From My iPhone on the pop-up box to remove the email account.
If you are inundated with email notifications from your other email accounts, disable the Mail app's notifications from the Notifications section of the Settings menu. Open the Settings screen, select Notifications, tap Mail and then slide the Allow Notifications switch to the Off position.