Use this method if you are a delegate for another user’s mailbox or when you have permissions to several folders in a shared mailbox. You can also use this method when you have full access permissions to a mailbox.

To open the shared mailbox:

1. Click Outlook in the top left corner of your screen.
2. On the Preferences menu, click Accounts > Advanced > Delegates.
3. Add the mailbox under Open these additional mailboxes

When you have Full Access permission to a shared mailbox—that is, Full Access permission of a mailbox set up through Exchange Admin Center (EAC) which can only be done by your Administrator—you can add the shared mailbox with your own credentials.