Dear Sir/Madam,
I am very keen to work on this project, mainly because I've done event photography just like this before. Granted, it was for 21st birthday parties and University events, but I'm sure that they're pretty similar. I understand that this is a pretty big event, and it's definitely a once in a lifetime party and I plan to make the photos as memorable for you as the night was.
Like I said, I've done similar events before so have no problem staying professional and getting those "in the moment" shots. Don't get me wrong, posed photos can be just as good, and if you wanted that we could even section off a small place just for posed photos (almost like a photobooth, have small props etc), but as you said, you know what you're looking for so in the end it's what you say that I'll aim for.
I hope that you will consider me for this job and feel free to contact me if you have any questions or if you wish to see examples of my work.
Kind Regards,
Song Lam