Outlook for Mac (new interface) not syncing / emails stuck in Outbox after macOS Tahoe 26.2 update

Question

Outlook for Mac (new interface) not syncing / emails stuck in Outbox after macOS Tahoe 26.2 update

Michelle 0

Since upgrading my MacBook to macOS Tahoe 26.2, the new Outlook for Mac desktop app has stopped working reliably. Emails stopped syncing, and outgoing messages get stuck in the Outbox. I've reset the account with no change. Outlook online and the legacy Outlook version both work fine, so I know this is an isolated issue with the new Outlook for Mac desktop app. Since Microsoft is retiring legacy Outlook for Mac in October, can this issue be troubleshot? "Switch to legacy" isn't a viable long-term fix.

Vimantha Fernando 0 Reputation points

2026-06-30T21:41:00.5533333+00:00
Hey, so this isn't just you, it's a known bug with the new Outlook for Mac app after the Tahoe 26.2 update. A bunch of people are dealing with it. Sync stops working and emails get stuck in the Outbox. Microsoft hasn't actually fixed it yet, but here's what's worked for people instead of just going back to old Outlook:

Outlook can look "up to date" but not actually be. Check Help → Check for Updates, and make sure Microsoft AutoUpdate is allowed to run in the background (System Settings → Login Items).

Basically a deeper reset than removing/re-adding your account. Quit Outlook, go to ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles in Finder, rename that folder, then reopen Outlook so it builds a fresh one and re-syncs your account from the cloud.

Quit Outlook, delete the files in ~/Library/Caches/Outlook, reopen.

Toggle "Work Offline" on then off again in the Outlook menu. Sometimes just kicks it loose.

If none of that works, jot down the Outlook version and any error you see under Window → Sync Errors, and use Outlook's Help → Feedback to report it...
Michelle 0 Reputation points

2026-07-01T04:58:31.5966667+00:00
Vimantha, I appreciate the insight on this ongoing matter. I've done the following based on your suggestions:

I've updated software from 26.5.1 to Tahoe 26.3.2, still experiencing issues. I've confirmed latest Outlook, via Apps. My Outlook Help drop down doesn't show "Check for Updates", see screenshot

I've reset Outook several times. Settings > Accounts > Manage > Reset Account. Should I remove account and re-add account?

I don't exactly know how to complete this suggestions - Quit Outlook, delete the files in ~/Library/Caches/Outlook, reopen. I used the help of Claude and did the following - Quit Outlook > Open Finder > Go > Hold down the Option (⌥) key > Clicked Library > Caches, BUT there was NO Outlook folder to Delete Cache.

I've toggled "Work Offline" several times

2 answers

Your answer

Vimantha Fernando 0 Reputation points

2026-06-30T21:41:00.5533333+00:00

Hey, so this isn't just you, it's a known bug with the new Outlook for Mac app after the Tahoe 26.2 update. A bunch of people are dealing with it. Sync stops working and emails get stuck in the Outbox. Microsoft hasn't actually fixed it yet, but here's what's worked for people instead of just going back to old Outlook:

Outlook can look "up to date" but not actually be. Check Help → Check for Updates, and make sure Microsoft AutoUpdate is allowed to run in the background (System Settings → Login Items).

Basically a deeper reset than removing/re-adding your account. Quit Outlook, go to ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles in Finder, rename that folder, then reopen Outlook so it builds a fresh one and re-syncs your account from the cloud.

Quit Outlook, delete the files in ~/Library/Caches/Outlook, reopen.

Toggle "Work Offline" on then off again in the Outlook menu. Sometimes just kicks it loose.

If none of that works, jot down the Outlook version and any error you see under Window → Sync Errors, and use Outlook's Help → Feedback to report it...
Michelle 0 Reputation points

2026-07-01T04:58:31.5966667+00:00

Vimantha, I appreciate the insight on this ongoing matter. I've done the following based on your suggestions:

I've updated software from 26.5.1 to Tahoe 26.3.2, still experiencing issues. I've confirmed latest Outlook, via Apps. My Outlook Help drop down doesn't show "Check for Updates", see screenshot

I've reset Outook several times. Settings > Accounts > Manage > Reset Account. Should I remove account and re-add account?

I don't exactly know how to complete this suggestions - Quit Outlook, delete the files in ~/Library/Caches/Outlook, reopen. I used the help of Claude and did the following - Quit Outlook > Open Finder > Go > Hold down the Option (⌥) key > Clicked Library > Caches, BUT there was NO Outlook folder to Delete Cache.

I've toggled "Work Offline" several times

Answer 1

Michelle 0

I just updated macOS from Tahoe 26.5.1 to Tahoe 26.3.2, and switched from Legacy Outlook to New Outlook to troubleshoot this issue. Unfortunately, the problem persists: emails are stuck in the Outbox and won't send, and email sync is not working correctly. Could you provide further guidance on how to resolve this?

Screenshot 2026-06-30 at 9.14.42 PM

0 comments

Answer 2

Dora-T 14,950 Microsoft External Staff Moderator

Hi Michelle

Thank you for reaching out to the Microsoft Q&A Forum and for sharing the details of your issue.

I noticed that Vimantha Fernando has shared several troubleshooting suggestions in the thread. If you haven't had a chance to review them yet, I recommend trying those troubleshooting steps to see if they help resolve the issue.

Additionally, I tested the same scenario in my environment using the new Outlook for Mac on macOS Tahoe 26.3.1 (a), and email synchronization and sending worked as expected.

User's image

If possible, you may want to consider updating to macOS Tahoe 26.3.1 (a) to see whether the issue has been resolved in the newer macOS version.

Please let me know how it goes. If you need any further assistance, please don't hesitate to let me know.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Michelle 0 Reputation points

2026-07-01T04:21:08.1233333+00:00

I've just updated macOS from Tahoe 26.5.1 to Tahoe 26.3.2, and switched from Legacy Outlook to New Outlook to troubleshoot this issue. Unfortunately, the problem persists: emails are stuck in the Outbox and won't send, and email sync is not working correctly. Could you provide further guidance on how to resolve this permanently?
Dora-T 14,950 Reputation points Microsoft External Staff Moderator

2026-07-01T06:04:25.91+00:00

Hi Michelle

Thank you for the update and for taking the time to share the troubleshooting steps you've already tried.

Please note that we're not Microsoft Support; this is a user-to-user community forum. Moderators here don't have access to your environment or Microsoft's backend systems, so we can only provide guidance based on public documentation and community experience.

I noticed that you mentioned removing and re-adding your account. I recommend trying that next to see if it makes any difference.

If the issue persists, you may also want to reinstall Outlook using the latest installer from the following Microsoft article: Update history for Office for Mac - Office release notes | Microsoft Learn

If reinstalling Outlook doesn't resolve the issue, another troubleshooting step would be to create a new macOS user profile and test Outlook there.

For your reference: Add a user or group on Mac - Apple Support

Note: This information is provided as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link.

If the issue continues after trying the above, I recommend opening a support ticket with Microsoft. Their support team has access to additional diagnostic tools to further investigate the issue. For further instructions, please refer to Get support - Microsoft 365 admin | Microsoft Learn.

Please note that contacting Microsoft Support requires an active Microsoft 365 subscription and the appropriate admin role (such as Global Administrator). If you’re an end user, please reach out to your IT administrator to raise the request on your behalf.

Thank you for your patience and cooperation.