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JanAdam's avatar
JanAdam
Copper Contributor
Oct 26, 2025

Outlook 365 (classic) freezes syncing subscribed folders via IMAP

Win 11 home, with all current updates.

Outlook 365 (365) Version 2510 Build 16.0.19328.20010) 64-bit; with all current updates.

ISP: telusplanet.net (which is Google, with limited functionality),

Servers: imap.gmail.com, port 993, SSL/TSL and smtp.gmail.com, port 465, SSL/TSL

Protocol: IMAP. I was using POP before without any problems for years.

The problem: When starting OL it downloads new mail messages OK. But after a while it freezes in ‘Synchronizing Inbox’ or rarely ‘Synchronizing Trush’ and does not download new messages from the server (which are visible in Gmail on Chrome) nor delete messages from the server, which were deleted locally. When this happens, to get it back, I need to shut OL down, wait, say 15 min, or longer, start it again and usually it is enough, occasionally I need to shut down and power the PC again. I have not uninstalled and reinstalled OL yet but am thinking of it.

I use IMAP to sync mail, and Sync2 for contacts, calendar, and tasks – that works OK.

I have tried just about anything possible, rebuilding profile, repairing OL, clearing cache, unlinking OneDrive, whatever I could think of, or what Copilot suggested, all to no avail. It is obviously very annoying. I believe, if it is happening to me, it must have had happened to others as well. It all started after switching from POP to IMAP.

Any suggestion will be greatly appreciated, Jan

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1 Reply

  • RobertSparnaaij's avatar
    RobertSparnaaij
    MVP
    Oct 30, 2025

    Since when are you experiencing this issue? When did it work correctly the last time?

    Which add-ins do you have installed?
    Disable the non-default ones (especially any security suite which integrates itself with Outlook) and try again.
    See; Enable/Disable add-ins - Robert 365

    Note that you are using an almost month-old Current Channel (Preview) release. There have been 5 new releases since then. Update to the latest build and see if you can still reproduce the issue. Also try using the non-Preview build and verify whether the issue goes away then.

    Things breaking or not working as expected can happen more frequently when using the Preview/Beta releases.

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