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Outlook freezing while sync/sending mail/receiving mail & periodically

Lorenzo 0 Reputation points
2025-08-27T11:40:42.1466667+00:00

Good day,

1 user is having an issue with sync issues.

When starting up out,closing outlook, sending mail receiving mail and when regular sync happens outlook disconnects from the outlook server. It happens 3 or 4 times a day and a full PC restart is needed to fix. All other 365 application work.

Troubleshooting steps taken:

Stable internet connection via ethernet.

No-one else onsite is having this issue.

Repaired config and profile.

Ticked and unticked cache mode.

Updated outlook,cleared outlook cache and emptied outlook sync folder.

To note:

One drive has shown no sync issues on the same pc.

When closing outlook via task manager there a multiple instances of outlook running while the "show hidden icons" tray shows a greyed outlook symbol trying to connect to server. Outlook needs to be closed via task manager though instance of application is not removed.

Outlook is not running in offline mode

Please assist

Microsoft 365 and Office | Office Online Server
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  1. Steven-N 6,595 Reputation points Microsoft External Staff Moderator
    2025-08-27T12:38:08.1866667+00:00

    Hi Lorenzo

    Thanks for reaching out to Microsoft Q&A forum support

    Based on your description, I understand that one user is experiencing recurring Outlook sync issues. Specifically, Outlook disconnects from the server during startup, shutdown, mail operations, and regular syncs, occurring 3 to 4 times daily. The issue requires a full PC restart to resolve, and while other Microsoft 365 apps function normally, Outlook remains unstable. You've already taken several troubleshooting steps, including repairing the profile, toggling cache mode, updating Outlook, and clearing cache and sync folders.

    The challenge appears to be related to persistent background Outlook processes and failed reconnection attempts. Multiple instances of Outlook remain active in Task Manager even after closure, and the system tray displays a greyed-out Outlook icon attempting to reconnect.

    This behavior suggests that Outlook may be hanging during shutdown or failing to release resources properly, which can interfere with subsequent launches and server connections. Since other users onsite are unaffected and OneDrive syncs without issue, the problem is likely isolated to the affected user's Outlook configuration or local environment.

    As a first approach, I recommend launching Outlook in Safe Mode using the command Outlook.exe /safe. This disables all add-ins and helps determine whether a third-party extension is causing the instability. If Outlook runs smoothly in Safe Mode, you can proceed with the following steps:

    • Disable add-ins via File > Options > Add-ins > Manage COM Add-ins.
    • Use the command Outlook /rpcdiag to open the Connection Status window and identify which service is failing.

    Hope my answer will help you, for any further support, kindly let me know

    If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".     

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