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Does Microsoft Outlook / Graph support preserving iCal UID when receiving calendar invites from other systems (e.g. Google Calendar)?

Dileep 20 Reputation points
2026-03-09T09:05:20.04+00:00

Does Microsoft Outlook / Microsoft Graph support preserving the iCal UID (RFC 5545 UID) from the originating system when a user receives a calendar invite from another calendar provider (e.g. Google Calendar, Zoom)?

Specifically:

  • When an event is invited from Google Calendar into an Outlook calendar, does Microsoft preserve the same UID so that the event’s iCalUId in Graph matches the sender’s iCalUID?
  • If not currently supported, is this on the roadmap or is there official guidance on how to correlate the same event across Outlook and other systems?

We need this for cross-platform deduplication and would like to know whether iCal UID preservation from other systems is supported or planned.

Thank you.

Microsoft 365 and Office | Development | Other
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  1. Dora-T 11,125 Reputation points Microsoft External Staff Moderator
    2026-03-09T12:18:46.5533333+00:00

    Hi Dileep

    Thank you for reaching out to the Microsoft Q&A Forum.

    Based on my research, the iCalUId property in Microsoft Graph is a read-only identifier generated and managed by Exchange to identify the same meeting across calendars within the Exchange/Outlook ecosystem (for example, the organizer and attendees’ calendars). Microsoft documentation does not indicate that the original RFC 5545 UID from external calendar systems is preserved when an invitation is received.

    As a result, when Outlook receives an invitation from another provider (such as Google Calendar), the iCalUId returned by Microsoft Graph may differ from the UID used by the originating system.

    There was previously a planned change related to iCalUId behavior, but it was later postponed, as mentioned here: Postponed- iCalUId update on Microsoft Graph - Microsoft 365 Developer Blog

    At this time, there is no publicly documented roadmap indicating that Microsoft plans to preserve external calendar UIDs as the iCalUId.

    Thank you for your understanding.

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