Yes, Lino sucks: he deprives me from sleep. But OTOH it’s really amazing: it took me less than an hour to solve the three remaining points:
sent_time field and refusing to send a second time.
preview of the mail that is about to be sent.
There can be more than one mail per Attendance: e.g. if confirmed is empty, we send an invitaton. Or more variants depending on status etc.