To write an interview follow up email to thank the interviewer and express your continued interest in the position, it is best to write the email as soon as possible after the interview, and be sure to address it directly to the person who interviewed you, not "To Whom it May Concern." Keep the letter brief and to the point, being certain to thank the interviewer for taking the time to meet with you and discuss the job. An interview follow up email can be a great way to remind the interviewer of the interview and show what kind of person you are, i.e. friendly and responsible.
Send an interview follow up email within a day or two after an interview. It is best to begin by simply thanking the interviewer for his or her time, and reiterating your interest in the position. You will want to briefly restate anything that was particularly important that was mentioned in the interview, such as specific skills or qualifications you possess that make you a good candidate for the job. You might also again state why you think you would be a good choice to be hired by the company, or something specific that you would bring to the position.
The key words to remember in an interview follow up email are "specific" and "positive." If the interviewer is on the fence about hiring you, a well written email that concisely details what you plan to bring to the company should you be hired might give you an edge. Also be sure that the message is politely enthusiastic; do not overdo it, but be clear that you are excited about the opportunity. Some people will say that a handwritten thank you note or card can be more effective than an email, but this will generally force you to write a much shorter message, and it can take a few days to be delivered to the person, whereas an email is instantaneous.
Keep your interview follow up email to under two or three short paragraphs, depending on the complexity of the job interview and what you have to say. Even if you just send a very brief note to communicate your appreciation, it will still be remembered favorably by the interviewer. Be sure to make the email look like a professional letter, including the address of the person who is receiving it as well as your own contact information. You might close by saying that you look forward to hearing from the interviewer or, if it seems appropriate, that you will be in touch in a certain period of time.