How To Change Default e-Mail Account (iPad)
If you have multiple e-mail accounts set up on your iPad (iPhone or iPod touch), you can set a “Default” account. This means that when you create a new message, it will send from the default account. When you Reply to or Forward a message, it will come from the account that the original message was sent to. This process shown on iOS 6, but it works the same in iOS 7.