iOS is the operating system software installed on your iPhone. To find out which version you have: Tap Settings, Tap General, Tap About, and view the version number.
Choosing a default email account for my mobile phone
If you've set up more than one email account on your mobile phone, you need to select a default email account. When you write emails, they'll automatically be sent from your default email account.
Tap Settings.
Tap Mail, Contacts, Calendars.
Tap Default Account.
Tap the required email account to use it by default.
When the box next to an email account is ticked (V), the account is set as the default email account.
