You have full access permissions to a shared mailbox
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)—you can add the shared mailbox with your own credentials.
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)—you can add the shared mailbox with your own credentials.
To open the shared mailbox:
On the Tools menu, click Accounts.
Click the Plus Sign to add an additional Exchange account.
In the E-mail address field, enter the email address of the shared mailbox.
Under Authentication, enter your own credentials.