Thank you letters are more than just a simply courtesy. They help remind the interviewer of your unique capabilities and value add and they allow you to reconnect with the hiring manager and deepen the relationship. If you interview with several people at one company, send each person a thank you letter and be sure to write something different in each one. You will quickly lose credibility with a hiring manager if you send the same letter to multiple recipients. A strong thank you letter can help you get to the next level in the interview process. so make sure to extend your appreciation to everyone you interview with.