Thanks forma the reply.
My understanding is that the server works as it should (when I sue Thunderbird, e-mail invitation to the guests are sent ad expected).
Looking at the link you kindly sent me, it seems, ifI’m not wrong, that the RSVP variable is set to false, by default. I suppose that it should become true when I add a guest to the event. How is it possible to double check this? When I look to the server side, the event created through davdroid is present, and the list of guests is present too, exactly how it happens when I use Thunderbird. But, in reality, with davdroid, the guests didn’t receive any notification.