The iCalUId returned by the Calendar event resource type in Microsoft Graph is defined as a unique, read-only identifier that is shared by all instances of an event across different calendars. It adheres to the RFC iCalendar specification of UID. It is an ID that is unique to a meeting or meeting series in case of recurring meeting. For example, an imported iCal meeting might have an iCalUId value of 19rh93h5t893h5v@calendar.iCloud.com.

Today, the iCalUId value returned by the calendar resource does not adhere to this definition. Instead, it returns a value that is unique for every instance of the event.

We plan to update the value that is currently returned in the property iCalUId to adhere to its definition and roll out the update by May 15, 2020.

If you use iCalUId to identify a specific instance of a recurring meeting, this scenario can be achieved by listing instances (occurrences) of an event with seriesMasterId for a specified time range.

If you have additional feedback, email us to let us know.