Add a Microsoft 365 Shared Mailbox as a Separate Account in Outlook Classic 2021 / 2024

This article explains how to add a Microsoft 365 shared mailbox as a separate Exchange account in Outlook.

This is different from the normal shared-mailbox method where the mailbox simply appears underneath your primary mailbox. When configured this way, Outlook treats the shared mailbox more like a separate account while still using your normal Microsoft 365 account to authenticate.

Before You Start

You must already have Full Access permission to the shared mailbox.

Important: If the shared mailbox already appears automatically in the Outlook folder list, do not add it again using this procedure until your IT administrator has confirmed that automatic mailbox mapping (automapping) has been disabled for your access.

If the mailbox is both automatically mapped and added as a separate Exchange account, it may appear twice or Outlook may behave unexpectedly.

You do not sign in using the shared mailbox password.

When Microsoft asks you to authenticate, you must sign in using your own primary Microsoft 365 account that has permission to access the shared mailbox.

1. Open Account Settings

In Outlook:

1. Click File.
2. Click Account Settings.
3. Click Account Settings again.
4. Select the Email tab.
5. Click New.

2. Enter the Shared Mailbox Address

When the Outlook setup window opens:

1. Enter the email address of the shared mailbox.

   Example:

   service@yourcompany.com.au

2. Expand Advanced options.

3. Tick Let me set up my account manually.

4. Click Connect.

Outlook may display Getting things ready for a short time.

3. Choose Microsoft 365

When Outlook asks which type of account you want to configure, select:

Microsoft 365

4. Sign In With Your Normal Microsoft 365 Account

Microsoft will now display a sign-in window showing the shared mailbox address.

Do not enter a password for the shared mailbox.

Instead:

1. Click Sign in with another account.

2. Enter the email address of your normal Microsoft 365 user account.

   Example:

   joe.bloggs@yourcompany.com.au

3. Click Next.

4. Enter the password for your normal Microsoft 365 account.

5. Complete MFA if requested.

Important: The shared mailbox address identifies the mailbox you are adding. Your normal Microsoft 365 account provides the authentication and must already have permission to access that mailbox.

5. If Windows Asks Whether to Sign In to All Apps

Windows may ask whether you want to use the Microsoft account to sign in to other applications and websites on the computer.

For a normal Outlook setup, choose:

No, this app only

This limits the sign-in to Outlook and avoids unnecessarily changing the Windows or Microsoft account configuration for other applications.

6. Choose the Outlook Cache Period

If Outlook displays the Cached Exchange Mode settings, use the download slider to select a reasonable amount of offline email.

For most users we recommend:

• 3 months, or
• 6 months

A smaller cache reduces the size of the local Outlook data file and the amount of email Outlook needs to download when the mailbox is first configured.

NOTE: The Cache mode may not be adjustable if your organisation has a fixed Group Policy set.

7. Finish the Setup and Restart Outlook

If the setup is successful, Outlook will display:

Account successfully added

Outlook will also advise that it needs to be restarted before the changes take effect.

1. Click Done.
2. Close the Account Settings window.
3. Completely close Outlook.
4. Reopen Outlook.

The newly added account may not appear immediately in Account Settings before Outlook has been restarted. This is normal.

8. Allow the Shared Mailbox to Synchronise

After Outlook restarts, the shared mailbox should appear as a separate mailbox in the left-hand folder panel.

Outlook may display a message indicating that it is preparing or updating the local Outlook data file.

Depending on the size of the mailbox and the cache period selected, it may take some time for the email and folders to finish downloading.

You can continue using Outlook while synchronisation completes.

Troubleshooting

The shared mailbox already appears in Outlook

The mailbox may have been automatically mapped by Microsoft Exchange because your account has Full Access permission.

Do not add the same mailbox again as a separate Exchange account until your IT administrator has disabled automapping for your access.

Outlook keeps asking for the shared mailbox password

Do not enter a password for the shared mailbox.

Choose Sign in with another account and authenticate using your normal Microsoft 365 email address and password.

Access denied or the mailbox will not open

Your Microsoft 365 account may not have the required permissions.

Contact your IT administrator and ask them to confirm that your account has Full Access permission to the shared mailbox.

If you also need to send email using the shared mailbox address, the administrator should confirm that you have the appropriate Send As permission.

The mailbox appears twice

This usually means the mailbox is being added both:

• automatically by Exchange automapping; and
• manually as a separate Exchange account.

Contact your IT administrator so automapping can be disabled before using the separate-account configuration.