If you've set up more than one email account on your mobile phone, you can select a default email account. When you send an email from one of your mobile phone's applications, the default account will be used unless you're asked to select an account before sending the email.
Tap Default Account.
Tap the required email account to select the email account as your default account.
Slide your finger upwards starting from the bottom of the screen to return to the home screen.