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MS Outlook running very slow after July 2025 update - how to fix?

Anonymous
2025-07-07T08:41:44+00:00

I am the account holder for my MS365 family account. MS Office updated last week (early July 2025) and classic Outlook in particular is extremely slow. Is there any way to improve this?

My system is an HP Spectre laptop. I use outlook to send and receive on three email addresses: one outlook.com, one gmail and one outlook exchange (I think - it's an official account for a school in the UK where I am a governor.) Until the update last week these had all been running fine.

Outlook | Windows | Classic Outlook for Windows | For business

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  1. Robert Sparnaaij [MVP] 18,296 Reputation points MVP Volunteer Moderator
    2025-07-11T19:18:14+00:00

    This issue appears to have been caused by a Teams update and its add-in for Outlook. A fix for it has been deployed to production and is 100% available now.

    When you update to the latest version of Teams and then restart Outlook, the issue should be gone.

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  2. Anonymous
    2025-07-08T18:14:47+00:00

    Hi Robert,

    Yes, it happens when I start in safe mode, but perhaps works a little quicker.

    Outlook is using practically no resources, as I would expect most of the time.

    The problem happens mainly when I am trying to open up calendar view. Quite often, the calendar pane is just white when I switch, or may have some appointments in but no gridlines of any description. I have to wait for it all to appear, or sometimes I get the message that Outlook is not responding and I've got the choice of waiting or restarting the app. Restarting the app doesn't make any difference so I wait.

    Everything works, but the calendar side in particular runs really slow as just described.

    Andrew

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  3. Robert Sparnaaij [MVP] 18,296 Reputation points MVP Volunteer Moderator
    2025-07-11T06:54:15+00:00

    What is the default Calendar set to and is that also the Calendar that you are experiencing issues with?

    What is the size of the calendar?
    Right click on your Calendar folder-> Properties-> button Folder Size...

    Check whether Cached Exchange Mode is enabled for your school account;
    File-> Account Settings-> Account Settings...-> double click on your Exchange Account

    Also, do you have any mailboxes or additional Calendars from colleagues added to your school account?

    There have been some Calendar related issues this week related to Outlook.com. These are fixed now but still rolling out to some areas.

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  4. Anonymous
    2025-07-11T01:23:36+00:00

    I'm experiencing the same issue. Primarily a delay on calendar load and when switching weeks with the < or > at the top of the calendar.

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  5. Robert Sparnaaij [MVP] 18,296 Reputation points MVP Volunteer Moderator
    2025-07-07T12:11:46+00:00

    Which exact actions are slow?

    Can you repro the issue when using Outlook in Safe Mode?

    Start-> type; outlook.exe /safe
    (note the space in the command above)

    When you open up Task Manager how many % CPU is Outlook using on average per minute?

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