Accessing a Shared Mailbox in Outlook 

Sign in to Outlook at outlook.office.com using your normal work account.

Select your profile picture or initials in the upper-right corner.

Select Open another mailbox.

[Enter the shared mailbox address]

Select Open.

Return to your own Outlook mailbox.

Right-click Folders in the left-hand folder list.

Select Add shared folder or mailbox.

[Enter the shared mailbox address]

Select Add.