The generic structures of formal invitation letters are ....
sender, receiver, opening, content (time, place, RSVP, etc.), and steps
sender, receiver, opening, content (time, place, RSVP, etc.), and closing
sender, receiver, opening, re-orientation, and closing
sender, conflicts, opening, content (time, place, RSVP, etc.), and closing
sender, receiver, opening, conflicts, and closing