I have been trying but am struggling to find any official documentation on this subject. I am using a system where I am manually creating ICS files and need to be able to track responses from recipients.
I have found that when I manually create an ICS file (rather than creating it in Google Calendar) and send that ICS file from one GMail account(the organizer) to another Gmail account, then no RSVP notification is received by the sender when the invitee accepts. However, when I send a manually created ICS file from a Gmail account to an Outlook account, an RSVP email is received by the sender when the invitee accepts. I have done a similar test where the sender is an Outlook account and discovered the same behavior.
Does anyone know how these systems work behind the scenes and if there is a way to force an email response, or to detect the RSVP responses in another way? Or perhaps an API to register a manually created invite with the provider?
I am positing that there is a sort of behind the scenes communication and alternate route that RSVP notifications take when the providers think that the invite was generated in their system, and that notification is essentially swallowed when the event doesn't already exist in their system.