Log Out of a Mail Account on an iPhone
1 Click on the settings Icon
Email settings can be accessed through the settings menu on the iPhone 6.
2 Choose mail, contacts calendars
After clicking on settings click on the 'mail,contacts,calendars' option.
3 Choose the email account you want
The iPhone has separate settings for each mail account that you use. If for example you want to turn off yahoo mail then choose the yahoo mail option.
4 Turn the mail button off
Inside the email account you chose there is an icon for the mail account with a toggle button. Turn the toggle button off so that the mail is stopped.
5 You won't be able to login
If you want to login again to your mail account you will have to turn the toggle button in once again. (See Why do some people love iPhones that much?)
6 Permanent deletion
In the same menu there is an option called 'Delete Account'. This option will delete that email account for good.
7 Repeat the steps for each email account
If you have multiple email accounts then repeat the steps for each of those accounts. (See Why people are buying the iPhone 7?)