Outlook Classic not opening properly or recording sent mails after 2026-01 Security Update (KB5074109) (26200.7623)

Chris Seagrave 350 Reputation points
2026-01-14T12:20:57.8233333+00:00

Hi,

I installed in the Windows Security update (KB5074109) (26200.7623) on 14th January 2026 and following this update Outlook Classic has a couple of problems.

The first is that when I first start my laptop Outlook Classic opens, but when I close it down I am now unable able to open it again as Office tells me it is still open. I can go into Task Manager and close the Background Process relating to Outlook Classic which allows me to open Outlook Classic again, but this is not ideal as I would rather not do this. Alternatively I can restart my laptop and Outlook Classic will open, but if I close it down it won't re-open unless I either close the Outlook Background Process in Task Manager or restart the laptop.

The second issue is that I can send an email and it will be sent to the person I am sending the email to, but it doesn't show as being sent in the Sent Items folder, this is very strange, receiving emails is fine so far.

I have encountered this using a Yahoo Pop account, so I need some guidance on what I can do to resolve these issues in Outlook Classic?

Is there a specific fix in Outlook Classic or do I need to uninstall this (KB5074109) (26200.7623) update?

I can't seem to find a way of uninstalling update (KB5074109) (26200.7623), so may need some guidance here?

Many Thanks,

Chris

Outlook | Windows | Classic Outlook for Windows | For home

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Answer accepted by question author
Suncoast Information Systems 315 Reputation points
2026-01-15T14:58:38.0166667+00:00

Uninstalling KB5074109 worked for us on several PCs

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Hornblower409 16,075 Reputation points
2026-01-25T03:29:40.27+00:00

January 24, 2026 - KB5078127 (OS Builds 26200.7628 and 26100.7628) Out-of-band
Fix for Outlook/OneDrive Issues.

https://support.microsoft.com/en-us/topic/january-24-2026-kb5078127-os-builds-26200-7628-and-26100-7628-out-of-band-cf5777f6-bb4e-4adb-b9cd-2b64df577491

I have installed KB5078127 and (so far) I am not seeing any problems.

Just resume your Windows Updates, check for updates, and it should offer you KB5078127.

As I understand it, you do not need to re-install KB5074109 if you previously removed it.

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  1. Noel Macadangdang 16,895 Reputation points Independent Advisor
    2026-01-14T14:31:54.5166667+00:00

    Hi,

    Thank you for sharing your question. It’s understandably frustrating when Outlook Classic doesn’t reopen properly and your sent messages fail to appear in Sent Items, especially when you’ve confirmed they’re delivered successfully.

    These behaviors appear to stem from how the update affected Outlook’s shutdown process and sent-mail handling. While there isn’t a specific hotfix released yet, here are some steps aligned with Microsoft’s guidance:

    Resolving the "Outlook is still open" message:

    Until an update is released to address this behavior, a viable workaround is to fully close any residual Outlook background processes before reopening the app or simply restart your device. A more lasting solution would be to repair your Office install, or rename the Outlook registry profile folder, which often resolves stuck background tasks.

    Ensuring mails are saved in Sent Items

    This is a common setting oversight or result of corrupted profile settings after updates. To verify:

    Go to File → Options → Mail, and ensure the option “Save copies of messages in the Sent Items folder” is checked.

    If it’s already enabled, the next step is to repair or recreate your Outlook profile—Microsoft reports this fixes many mail-sync issues.

    Uninstalling the KB5074109 update (if needed):

    If you prefer to remove the update temporarily, follow these steps:

    Open Settings → Windows Update → Update history → Uninstall updates, locate KB5074109, and choose Uninstall, then restart your PC.

    I hope this helps.

    Best Regards,

    Noel

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  2. Bill P 10 Reputation points
    2026-01-25T01:17:52.47+00:00

    Microsoft just announced a new OOB update to fix the Outlook and other issues. I have not tried it yet due to time constraints if something should go wrong. January 24, 2026—KB5078127 (OS Builds 26200.7628 and 26100.7628) Out-of-band

    https://support.microsoft.com/en-us/topic/january-24-2026-kb5078127-os-builds-26200-7628-and-26100-7628-out-of-band-cf5777f6-bb4e-4adb-b9cd-2b64df577491

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  3. Hornblower409 16,075 Reputation points
    2026-01-20T05:35:17.5333333+00:00

    [Updated 2026-01-20 with link to official Microsoft Instructions]

    @TamakoTakamatsu-6777 said

    I tried uninstalling the update, but then got nervous about the purported security risks

    There is an other alternative that may work for you. You have to move all of your Outlook PST files out from under your OneDrive folder.

    How to remove an Outlook .pst data file from OneDrive
    https://support.microsoft.com/en-us/office/how-to-remove-an-outlook-pst-data-file-from-onedrive-b6b9e522-59bd-40f7-949f-168d0aa9b38e

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