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Outlook for Mac on Microsoft 365 stops auto-syncing after initial sync and does not appear in macOS Login Items background activity list. I believe this needs to be reset from your account's push notification token on your end,
Using the New Outlook for Mac for personal email and calendar
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Thank you so much. As it turns out the issue was that I had 4000 emails in my Delete folder and after the network went out it took a long time to rebuild. Then all the reinstalls started the Delete folder to re-build and begin all over again. Having left the laptop for a day, when I returned it worked. I offer this so the community might learn from my neglect.
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Hi daniel,
Thank you for sharing the update. I’m glad to hear Outlook is syncing again.
It sounds like the large Deleted folder caused Outlook to spend a long time rebuilding after the network interruption, and repeated reinstalls may have restarted that process. Your feedback will be helpful for others who run into similar behavior.
Thank you again for posting the outcome.
Hi daniel,
Welcome to Microsoft Q&A forum.
Sorry you’re dealing with this. Microsoft does have a published issue for Outlook for Mac and Outlook Mobile intermittently stop syncing, currently listed as investigating. If Outlook is showing the exact sync-mailbox error, Microsoft’s workaround is to open Outlook on the web > People > Favorites and delete all Favorites contacts.
Please note that this is a user-to-user support forum. Moderators, contributors including external Microsoft employees cannot directly intervene in Microsoft product features or access back-end systems. Our role is limited to providing technical guidance on reported issues, requests, or ideas only.
You can also try these Microsoft-documented checks:
Please feel free to let me know if you have any further updates, thanks.
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That wasn't my issue. My problem isn't intermittent. After an wifi issue, outlook stopped syncing automatically but would sync manually. I wonder about a corrupted file but I've reinstalled it several times, removed it, reset it etc. I can't get it to work.
Hi daniel,
Thanks for the clarification. Since manual sync still works, I’d focus on the Mac client side first. Please check that Work Offline is not enabled, review the account status in Tools > Accounts, and test the mailbox in Outlook on the web. If this is an Exchange / Microsoft 365 account, you can also try Reset Account or Empty Cache to rebuild the local sync data, since a corrupted cache can cause sync problems.
Thank you. There is new information I discovered. Outlook is not shown in Apps Running in the Background and in Activity Monitor there are no files under Microsoft.
Hi daniel,
Outlook not appearing under macOS Login Items / Background Activity does not always confirm that Outlook is missing a required file or component. However, if Outlook stops syncing automatically after a network issue and only syncs when manually triggered, it could point to a local Outlook profile, cache, or background process issue. At this stage, I recommend using Help > Contact Support directly from Outlook for Mac, as the Outlook support team can review diagnostic logs and check whether the client is failing to refresh or run background sync properly.
Please also include your Outlook for Mac version, macOS version, account type, and mention that manual sync works but automatic sync does not.