Thank you note etiquette is confusing. Miss Manners states that the proper response to a spoken "thank you" is always "you're welcome." But what happens when the thank you is written? There are no time-honoured guidelines for responding to a thank you note, and most people do not bother to reply to such a note. However, in some situations the sender of the thank you might appreciate a reply.
Consider if it is worth sending a reply. In the United States you are not obligated to reply to a thank you note, but it may leave a positive impression with the sender of the note. Imagine, for example, the job candidate who sent thank you notes to all of the companies that interviewed her and received no acknowledgement in return. She is probably imagining the worst; that her interviews went horribly. You sending a note does not indicate that she was hired or even that her interview went well, but it may mean a lot to her that you thought enough of her to reply.
Decide how you would like to reply. Your response to the thank you doesn't need to be formal; you can reply via e-mail if it is someone that you have exchanged e-mails with before. Alternately, a simple handwritten note will suffice if you prefer to add a touch of formality. If you are responding to a thank you from a family member, a phone call is fine as well; for example, if your niece writes you a nice thank you for her birthday gift you may call and tell her you appreciated her note and inquire if she has used her gift yet.
Respond to the thank you. Your response should be short and sincere. For example, if you are responding to the thank you note sent by a job candidate whom you have just interviewed, you may state something like "Dear Jane, It was nice meeting you as well; I enjoyed talking with you last Wednesday. I will be in touch soon about your application. Sincerely, Bob Smith." A note written to your son's Boy Scout troop might read "You are very welcome; it is a pleasure to see that young people are still being taught manners."
Do not expect a reply after you send your response. If you do receive additional correspondence, don't feel obligated to answer it.