Access a shared mailbox in Outlook

1. In classic Outlook, select File > Info > Account Settings > Account Settings.

2. On the Email tab, choose your email account and select Change.

3. Select More Settings > Advanced > Add. Enter the email address of the shared mailbox and select OK and OK again.

4. Select Next > Done > Close.

For more info, see Open and use a shared mailbox in Outlook.

1. Note: Currently, in the new Outlook, you can only add a shared mailbox as a resource, not as an account. However, a future update is planned to support this feature. ( Roadmap for Shared Mailboxes as Accounts in new Outlook )
   
   For new Outlook​​​​​​​, in  Mail, in the left folder pane, right-click your account name, then select Add shared folder or mailbox.

2. In the Add shared folder or mailbox dialog, type the name or email address of someone who has shared a mailbox with you, and then select Add.

The shared mailbox appears in your Folder list on the left. To remove it, you can right-click the shared mailbox, and then select Remove shared folder.

For more info, see Open and use a shared mailbox in Outlook.