Ooooo I think one paragraph is plenty. The ones I get are usually not any longer.
Dear X,
Thank you so much for taking the time to interview me for XSOM. I really enjoyed hearing your take on the special thing you're interested in. I feel like your school is a great fit for me because XYZ. Thank you again for your time and effort!
Have you ever wondered how you should go about contacting an interviewer after a medical, dental, veterinary, or podiatry school interview? Although it