An all-day event in outlook calendar in IST is not converted to UTC while fetching the events using graph API with prefer in headers as 'Prefer': 'outlook.timezone="UTC"', while other events do. Why?

Question

In an outlook calendar with timeZone IST, an all-day event is created on 22nd March and a normal event is created for 8:00AM to 8:30 AM on the same day.

When the events are listed using graph API to list the events with:
'Prefer': 'outlook.timezone="UTC"',

for normal event it is listed as,
start:{dateTime: 2023-03-22T02:30:00.0000000, timeZone: "UTC"} .
But for the all-day event, it is shown as
*start:{dateTime: 2023-03-22T00:00:00.0000000, timeZone: "UTC"}. Similarly for the end too.
*
Why is it like that? Why is an all-day event not getting converted to the preferred timeZone while it shows the timeZone as UTC in the response?

Answer 1

Hello Jessal John Mammen,

Thanks for reaching out!

While listing events using Microsoft Graph API, it is an expected behavior that the startDateTime and endDateTime will return in UTC format.

Adding Prefer: outlook.timezone="India Standard Time" into the Request Header will provide the response in IST Time Zone.

Please refer to the below screenshots:

Hope this helps.

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