To send a new e-mail from a shared mailbox follow these steps.

Notes! 
- You must be a member of the shared mailbox to have permission otherwise the mail will fail with an error.
- This only applies to sending new e-mails from a shared mailbox. If you are in the existing shared mailbox reading and replying to e-mails you can simply click the reply button.

1. Click "New Email".
2. If the From box is not showing click the "Options" tab and click the "From" button to enable it.

3. Click the From button on your new e-mail and choose "Other E-mail Address...

4. On the dialog that pops up click the "From..." button

5. Click the drop down on the Address Book and chose "Global Address List".

6. Find the e-mail you want to send from in the list and highlight it then click OK

7. Now populate and send the e-mail out as normal. It will now be sent from the specific shared mailbox address on behalf of your main e-mail.