Outlook Calendar

Availability comes from a single Microsoft Graph call, /me/calendar/getSchedule, asked for every required host's connected mailbox. Graph answers for a mailbox it cannot see with an empty row rather than an error, and an empty row is indistinguishable from a free calendar, so a mailbox that returns nothing is treated as unknown, not as available.

When the booking is confirmed, Setupp creates one event on the connected mailbox with every host as a required attendee and the booker alongside them. Microsoft sends the invitation from its own systems, the same way Google does for a Google host.

Times are sent to Graph as naive local values with the timezone named separately. Sending an offset as well makes Graph apply the zone twice and lands the meeting hours away from where it was booked. That is the single most common way a Microsoft calendar integration goes wrong.

Cancelling in Setupp deletes the same event, so the withdrawal reaches every attendee the way the invitation did. Tokens refresh ahead of expiry and are written back.