1. Open a new Email
2. Go to the Options tab at the top of the new email
3. Press the “From” option under Show Fields
4. In the email, press the drop-down menu under from and select Other Email address..
5. Press the From… in the menu box
6. Find the address you want to send as, press it and then press OK
7. Press OK again
8. The email will now be sent as the other mailbox