Understanding iCal UID in Microsoft Calendar Events.

Overview

When dealing with calendar events in Microsoft, it is essential to understand how the Event ID and iCal UID work. Users may notice that the Event ID for the same calendar event can differ across various users. This article explains why this happens and how to handle this situation using the iCal UID.

Event ID Behaviour in Microsoft Calendars

Each calendar event in Microsoft has a unique Event ID assigned to it. When multiple users are invited to the same meeting, each user receives their own unique Event ID for the same calendar event. This behavior is provider-specific, and Nylas returns this value directly from the provider.

Handling Event Deduplication

To avoid issues like sending updates for the same meeting through your application, you can use the iCal UID instead of the Event ID. The iCal UID is unique across all participants, including the organizer, for the same event.

Recurring Meetings and iCal UID

For recurring meetings, each instance of the event will have its own unique iCal UID. This UID will be consistent across all participants for that specific instance of the recurring event.

The master event will also have its own iCal UID, which will be the same across all participants but different from the instances (child events).

Special Case: Cross-Platform Events

When events are created from Google (Organizer) and involve Microsoft (Participants). In this scenario, Microsoft may encode the iCal UID in hexadecimal. Nylas is working on improvements to handle this encoding, but technically, they represent the same iCal UID.

Conclusion

The iCal UID is a reliable way to identify unique calendar events across different participants and instances. By using the iCal UID, you can ensure that your integrations handle events consistently and avoid duplication issues.

Note: For Google grants all the recurring instances share the same ical UID. Users can simply use event ID as unique identifier across grants.