If you've set up more than one e-mail account on your mobile phone, you can select a default e-mail account. When you send an e-mail from one of your mobile phone's applications, the default account will be used unless you're asked to select an e-mail account before sending the e-mail.
Find "Default Account"
Press Mail, Contacts, Calendars.
Press Default Account.
Select default e-mail account
Press the required email account until it has been selected as the default account.
Return to the Home screen
Press the Home key to end the session and return to the Home screen.