How do I add someone else's hosted Exchange mailbox to my Outlook profile?

This article describes how to add someone else's mailbox to your existing Outlook profile that's already connected to a hosted Exchange mailbox.

WARNING: You need to have appropriate permissions to the mailbox in order to be able to add it. If you need to adjust permissions, please open a support ticket.

WARNING: The mailbox you are adding should not be hidden from the Global Address List (GAL).