Baïkal tries to solve that by sending out the ics for you, it'll even accept responses in various formats (inviting to calendar events seem to be poorly standar

Baïkal tries to solve that by sending out the ics for you, it'll even accept responses in various formats (inviting to calendar events seem to be poorly standardized). Last I played around with it it all worked, somewhat. It does require you to use baïkal as your caldav server though.