2.3. Change Your From Address

The From address of an outgoing message is the address that the recipient will see the message as being from and, thus, the address at which you’ll receive any reply. If you have configured more than one email address or account, Mail normally uses the From address associated with the mailbox you’re viewing when you create the email message. When you create the message while in the Accounts view, or from within another app, the From address is ordinarily the main email address of your default account (see Other Mail Settings). However, you can choose a different From address for any given outgoing message, with some qualifications.

In general, here’s what you do: