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How to Fix Outlook Resending Previously Sent Calendar Invitations
Question details
Users are experiencing an issue where Outlook randomly resends calendar invitations that were already sent, leading to duplicate notifications for recipients.
- Product
- Microsoft Outlook / Microsoft 365
- Device & OS
- not provided
- Scenario
- Managing calendar events and notifications after recently moving or migrating to Microsoft 365.
- Observed behavior
- Outlook randomly resends previously sent calendar invitations on its own, causing unwanted duplicate notifications for the invitees.
Ensure you have administrator privileges for your Microsoft 365 tenant, as resolving this backend issue requires accessing the admin center to contact Microsoft Support.
Open a Service Request in the Microsoft 365 Admin Center
Because this issue relates to backend server behavior after a Microsoft 365 migration, opening a dedicated service request is the most effective way to resolve it.
This glitch typically stems from synchronization or backend routing issues that cannot be resolved through standard client-side troubleshooting. Microsoft Support engineers will need to collect advanced logs from your tenant to investigate and fix the behavior.
Log into the Microsoft 365 admin center using an account with appropriate administrator permissions.
On the left-hand navigation menu, click on 'Show all', then select 'Support'.
Click on 'New service request' from the available support options.
Describe the issue explicitly, noting that old calendar invitations are being randomly resent post-migration. Provide your contact details and select 'Contact me'.
Contact Microsoft Support via Phone
Use this method if you are unable to access the Microsoft 365 Admin Center or if you prefer to speak directly with a support agent regarding your tenant.
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Frequently Asked Questions
Why is Outlook suddenly resending old calendar invitations?
This issue is most commonly seen after migrating email accounts to Microsoft 365. It is usually caused by backend synchronization glitches where the server incorrectly flags historical calendar items as unsent or updated, triggering duplicate notifications.
Can I fix this issue by clearing my Outlook cache?
No. Because this specific bug originates from Microsoft 365's backend server behavior rather than the local Outlook client, clearing your cache, reinstalling the app, or working offline will not permanently resolve the issue. Microsoft Support must investigate the tenant.
What information should I gather before contacting Microsoft Support?
To speed up the investigation, gather the exact dates of your migration, the email addresses of affected users, screenshots of the duplicate invitations received by attendees, and the message headers of the resent invites.
Will attendees keep receiving these duplicate invitations until it is fixed?
Unfortunately, yes. The backend server will continue to process these sync errors until Microsoft engineers apply a fix to your tenant. Informing your team to ignore the duplicates temporarily is the best interim workaround.
