Microsoft 365 Outlook for Mac isn't syncing

Microsoft has not identified a sync issue specific to macOS 27.2.1, so first test the mailbox in Outlook on the web and then repair the local Outlook connection if web mail works normally.^1^

1. Determine whether the problem is Outlook or the mailbox

1. Open Outlook on the web and sign in with the same Microsoft 365 account.
2. Send yourself a test message.
3. Check the result:
   • Web mail also fails: this points to a mailbox, Microsoft 365 service, or organizational connection issue. Contact your Microsoft 365 administrator.
   • Web mail works: continue below; the issue is local to Outlook for Mac or its connection.

In Outlook, select Tools > Accounts and select the Microsoft 365 account. An orange status indicator means Outlook is not connected to Exchange. Also open the Outlook menu and ensure Work Offline is not selected.^2^

2. Update Outlook after the macOS update

Updating macOS does not necessarily update Outlook.

• If Office came from Microsoft:
  1. Open Outlook or Word.
  2. Select Help > Check for Updates.
  3. Install all available Microsoft updates.
  4. Restart the Mac and test Outlook.
• If Outlook came from the Mac App Store:
  1. Open App Store > Updates.
  2. Select Update beside Outlook, or Update All.^3^

3. If web mail works but Outlook still does not sync, reset the account cache

This causes Outlook to download the mailbox again from Microsoft 365.

Caution: Resetting the account deletes Outlook data that has not yet synchronized to the server. Check for unsent drafts or locally stored items first.

1. Confirm the Mac has a stable network connection.
2. In Outlook, select Tools > Accounts.
3. Select the affected account.
4. At the bottom, select Manage > Reset Account.
5. Leave Outlook open while the mailbox downloads again; large mailboxes can take considerable time.^4^

Avoid repeatedly removing the account while it is rebuilding, because that restarts the download.

4. If you see “We’re having trouble syncing the mailbox”

Microsoft is investigating an intermittent issue with that exact Outlook for Mac message. Its documented workaround is:

1. Open Outlook on the web.
2. Open People.
3. Under your mailbox, select Favorites.
4. Delete all contacts listed in Favorites.
5. Restart Outlook for Mac and test synchronization.^5^

Use this workaround only when the displayed message matches; it is not documented as a general fix for every sync failure.

5. If it remains unresolved

Capture a short synchronization log before contacting Outlook support or your Microsoft 365 administrator:

1. In Outlook, select Window > Sync Errors.
2. Select the gear icon.
3. Enable Turn on logging for troubleshooting.
4. Restart Outlook, leave logging enabled, and reproduce the problem.
5. Quit Outlook, then restart it and select Turn Logging Off.

Do not leave logging enabled because the log files continue growing.^6^

Report the Outlook version/build, whether Outlook on the web works, the account’s connection indicator, the exact sync error, and when synchronization last succeeded. In Outlook for Mac, support is available from Help > Contact Support.^1^

References

1. Fixes or workarounds for recent issues in Outlook for Mac
2. I can't connect to my Exchange account in Outlook for Mac | Microsoft Support
3. Update Office for Mac automatically
4. Clear the cache in Outlook for Mac | Microsoft Support
5. Outlook for Mac and Outlook Mobile intermittently stop syncing
6. Enable logging in Outlook for Mac