Hi i have been invited to a regimental cocktail party, but am a bit confused on the best way to RSVP to the event. is it best to write a formal letter just saying that i will be attending? do i start the letter with sir? (RSVP the adjutant). sorry for stupidity but never had to RSVP anything to do with the military before (I am 19 btw). Thanks for any help.