I am trying to get my zimbra server to reschedule an appointment via REST.
curl -v -u us@er.pro:123456 --upload-file file.ics http://er.pro/service/home/us@er.pro/Cal1?fmt=ics
It is relatively straight forward, file.ics is updated with new date of the VEVENT maintaining the UID, incrementing the SEQUENCE and updating the DTSTAMP. I post the ics with curl and the appointment is updated. Easy-peasy.

Now if I had attendees (required participants) to this event then they need to be notified of this change. I.e. new invites need to be sent out to them. On the smartclient the ModifyAppointmentRequest SOAP call does that, but with my REST call this notification is not happening. The event is only updated in the organiser's calendar but not in the attendees' calendars.

I have read RFC 2446 - iCalendar Transport-Independent Interoperability Protocol (iTIP) Scheduling Events, BusyTime, To-dos and Journal Entries but it is still not clear what method should be used in my ics. A REQUEST is the obvious choice as per but my understanding is that it is for the communication between the servers. What method would the organizer's client use when talking to the server?