Outlook Desktop on Mac Cannot Access Shared Mailbox

Hi Rmusic

Thank you for reaching out to the Microsoft Q&A forum regarding the issue of being unable to access a shared mailbox on the Outlook for Mac desktop application.

Based on your description, I understand that the shared mailbox is accessible via Outlook on the Web and mobile devices but not on the Mac desktop client, despite confirming the admin settings are correct. This is a common scenario, and it usually points to a configuration or profile issue within the local Outlook application itself rather than a problem with your Microsoft 365 permissions. And here are some recommended solutions you can try:

Option 1: Manually Add the Shared Mailbox

The method for adding a shared mailbox is different depending on whether you are using the "New Outlook" or "Legacy Outlook" for Mac.

• If you are using the "New Outlook":
  • In Outlook, right-click on your primary mailbox name in the folder pane (the left-hand column) > Select "Add Shared Mailbox..."
  • Enter the email address of the shared mailbox and click Add.
• If you are using "Legacy Outlook":
  • In the top menu bar, click Tools > Accounts.
  • Select your primary account from the list on the left > Click the Delegates & Sharing, then select the Delegates tab.
  • Under the section "Open these additional mailboxes," click the plus (+) icon.
  • Search for and add the shared mailbox, then click OK.

After completing these steps, please restart Outlook and check if the mailbox appears.

Option 2: Clear the Cache for the Shared Folder

If the mailbox was added but you cannot see its contents, a corrupted cache might be the cause.

Clear the cache in Outlook for Mac - Microsoft Support

Option 3: Create a New Outlook Profile

Your current Outlook profile may be corrupted. Creating a new one will force Outlook to download a fresh copy of your mailboxes from the server. (Close Outlook and all other Microsoft Office applications)

• Open the Finder, go to the Applications folder, and find Microsoft Outlook. Right-click on the Outlook icon and select "Show Package Contents."
• Navigate to Contents > SharedSupport. > Double-click the "Outlook Profile Manager" application.
• Click the plus (+) icon to create a new profile, give it a name (e.g., "New Profile [Date]"), and click OK.
• Select the new profile you just created and click the gear icon to "Set as Default."
• Close the Profile Manager and launch Outlook. You will be prompted to set up your primary email account again. Once your account is fully synced, check if the shared mailbox has appeared automatically.

If none of the solutions above resolve the problem, please reply to this email with the following information so we can investigate further:

• Outlook Version: Are you using the "New Outlook" or "Legacy Outlook"?
• Error Message: When you try to access the mailbox, do you receive an error message? If so, please share the exact text of the message or error screenshots, so I can better understand the issue. Kindly blur or hide any sensitive information in the image.
• Software Versions: Please provide the specific version numbers for macOS: (Click the Apple menu > About This Mac) and Outlook for Mac: (In Outlook, click Outlook > About Outlook)

I look forward to your response.

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I had the same problem today, and found a workaround. (I was using the new/current version of Outlook when I came across the issue - couldn't add the shared mailbox using the dialog in settings, and had previously found that I could access the mailbox on Outlook for the Web, so confirmed it was indeed working elsewhere):

I double-checked that the shared mailbox was correctly shared with the user in the admin portal (ask your admin to to this if you can't yourself) and then I did the following:

1. Revert Outlook Mac to the Legacy version.
2. Outlook will close and re-open
3. In the Legacy version, go to the menu bar select Outlook > Settings...
4. On the Outlook Settings dialogue and choose Accounts
5. For the account you want to have access to your shared mailbox, click Advanced in the bottom right-hand corner.
6. Select the Delegates tab
7. Go to the lower section titled Open these additional mailboxes and click the plus (+) icon.
8. Search for and add the shared mailbox, then click OK.
9. Close and re-open Outlook

After this, the mailbox started to appear in the Legacy version of Outlook as a shared mailbox in my colleague's profile. It may take some time to appear, so give it a couple of minutes before checking if it doesn't happen instantly. To return to the new/current version:

1. On the menu bar select Outlook > Legacy Outlook
2. The dialog will ask you to confirm the change. Choose Switch to Outlook (This will cause Outlook to restart again.)
3. When Outlook restarts go to the menu bar and select Outlook > Settings
4. Choose Accounts
5. Select the account with your Shared Mailbox
6. Under Delegates and Sharing your shared mailbox should appear here now.

If you have multiple accounts associated with your Outlook, check to see that the shared mailbox appears under the 'All Acounts' profile (usually a globe symbol in the top left of new/current Outlook). If it appears there, but not on your desired profile, go to Outlook > Settings > Profiles and tick the box for your shared mailbox under the profile(s) you wish it to appear on.

I genuinely hope this helps someone, as this was quite the head-scratcher!

Thanks!