Outlook Calendar

Availability comes from Microsoft Graph's calendarView on each host's own connected calendar, over the dates being offered, asking for nothing but each event's start, end, show-as status, whether it is cancelled and whether it lasts all day. Recurring meetings come back as their separate occurrences. It works the same for work, school and personal Microsoft accounts. Every page of the answer has to arrive: a calendar read only in part, or not at all, is treated as busy rather than 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 cancels the same event through Outlook, so the withdrawal reaches every attendee the way the invitation did. Tokens refresh ahead of expiry and are written back.