Receiving calendar meeting invite acceptances repeatedly, some for past meetings.

Question

getting calendar meeting invite acceptances repeatedly - some for past meetings, repeatedly coming through. I am using the old outlook and some are using the new outlook.

Answer 1

Hi @Emi,

Thank you for reaching out regarding the repeated meeting acceptance emails you’re receiving, including those for past meetings. I understand how disruptive this can be, especially when users are working across both classic and new Outlook experiences.

Please try the following steps to help identify and fix the issue:

 

 

1/ Check Outlook on the web to isolate the issue

Open Outlook on the web: https://outlook.cloud.microsoft

• If the repeated responses do not appear in the web version, the issue is likely related to your local Outlook client (cache/OST).
• If they appear in both web and desktop, it may indicate an actual flood of responses, often caused by a syncing issue or a device repeatedly sending responses.

 

2/ Ensure Outlook is up to date

Please ask any affected attendees to make sure they are using the latest version of Outlook, especially if they are accessing their mailbox from mobile devices (iOS or Android).

Outdated apps can sometimes cause sync issues, which may result in repeated meeting responses being sent unintentionally. Updating to the latest version helps ensure proper synchronization and can often resolve this type of behavior.

 

3/ Reduce inbox clutter (classic Outlook)

In classic Outlook for Windows:

• Go to File > Options > Mail > Tracking
• Enable:
  • Automatically process meeting requests and responses
  • Update tracking information, and then delete responses that don’t contain comments

This helps prevent your inbox from filling up while still maintaining tracking accuracy.

For reference: Change how Outlook processes read receipts and meeting responses ...

4/ Clear local calendar cache (classic Outlook)

This can resolve sync loops:

• Close all Office apps
• Open Outlook > Calendar
• Right-click your calendar > Properties
• On the General tab, select Clear Offline Items > OK

This forces Outlook to download a fresh copy from the server.

For reference: Outlook shows conflict errors when updating or cancelling meetings ...

 

If the “Clear Offline Items” option isn’t available:

Method 1: Rebuild the OST (delete the cache so Outlook re-syncs)

• Close Outlook
• Press Windows + R, then enter: %LOCALAPPDATA%\Microsoft\Outlook\
• Locate your .ost file
• Rename it (e.g., .ost > .old) or delete it
• Reopen Outlook and allow it to fully re-sync

Note: If you previously made changes while offline that haven’t synced to the server yet, rebuilding the OST may cause you to lose items that exist only locally. (That’s why renaming first is safer.)

 

Method 2: Run a command to clean the “processing pipeline,” then sync again

You can also try clearing internal processing:

• Close Outlook
• Press Windows + R, then run: outlook.exe /cleanips
• Reopen Outlook and perform a full sync

 

If the issue continues, I recommend contacting your IT administrator to review the issue further or open a support ticket through the Microsoft 365 Admin Center for deeper investigation.

In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support  

I hope this helps. Please try these steps and let me know how it goes. If the issue persists, we can continue working together to find a solution.

As other users will also search for information in this community, your vote can significantly help those with similar inquiries quickly locate the most relevant resources. 

Thank you for your kindness and for contributing to the forum.   

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Answer 2

Repeated or duplicate calendar responses (including for past meetings) are typically caused by known Outlook calendar issues or temporary service incidents.

Based on the available information, there are two main possibilities and corresponding actions:

1. Service-side issue or client bug (especially Outlook mobile / new Outlook / Android)
   There is a documented incident where Outlook for Android caused past calendar invites to reappear and retrigger activity due to a sync bug in specific builds (for example, build 5.2609). This led to past invites resurfacing unexpectedly. The fix was rolled out in later builds (5.2610.1 and higher), and impact reduced as clients updated. What to do:
   • Ensure all attendees (especially those on mobile or new Outlook) are on the latest Outlook client versions. Ask affected users on Android/iOS/new Outlook to update their Outlook apps from their app store and restart the apps.
   • If the issue is recent and widespread, check your Microsoft 365 Service Health dashboard for any active calendar-related incidents similar to EX1259209 and monitor until resolved.
2. Calendar data conflicts / duplicates in classic Outlook
   If classic Outlook is involved and there are underlying calendar conflicts or duplicated items, Outlook can repeatedly sync and reprocess meeting responses. A supported mitigation is to clear and resync the local calendar cache so Outlook pulls a clean copy from the server:
   1. Close Outlook and all other Office apps.
   2. In classic Outlook, go to the Calendar pane.
   3. Right-click the main Calendar folder and select Properties.
   4. On the General tab, select Clear Offline Items and then OK.
   5. Restart Outlook and allow it to fully resync the calendar.
   Notes:
   • This clears only the local OST copy of calendar items; the server copy remains and is resynced.
   • If an error appears when clearing offline items (for example, OST in use), restart the machine and try again, or create a new Outlook profile so a fresh OST is built.

If repeated responses are only for a small set of meetings and not continuing to grow, they may be residual effects of a past incident; in that case, updating clients and allowing some time for service-side cleanup is usually sufficient.

If the behavior continues after client updates and clearing the local calendar cache, collect specific examples (meeting ID, organizer, affected attendees, timestamps, and client versions) and open a support case so Microsoft can check for any current service incident affecting your tenant.

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References:

• Outlook shows conflict errors when updating or cancelling meetings
• Meeting requests are re-triggered as updates from Outlook mobile without user intervention - Microsoft Q&A