If you use different email addresses for your messages (e.g. one for work, one for private correspondence), you may want to be able to use those also on your iPad, iPhone, or iPod Touch.

It is not necessary to add a complete email account for each of them, though.

Rather, you can just insert them into the Email Address field of any of your email accounts, separated by commas, like jane@example.com, jane.doe@example.net.