This requires that permissions be set in MyExchange and then using the Open Another Mailbox feature in OWA.
- First Follow the steps found on how to Grant Send-As permissions in MyExchange
- Log in to OWA using your own mailbox email address and password.
- Click on your name in the upper right corner of the window and click Open Another Mailbox.
- In the Open Other Mailbox box, enter the email address of the mailbox that you want to open and click Open. The mailbox will open in a new window.