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 the main menu icon.
Slide your finger right starting form the left side of the screen.
Tap the required email account.
Tap the menu icon.
Tap General settings.
Tap Set as default account to select the email account as your default account.