Why is it important?
Really, why does it matter? Sending a thank-you is another way for your interviewer to learn more about you. Are you thoughtful or do you just send a form thank-you? (Don’t do that, by the way.) If you incorporate personal and specific elements, which you should, it will show that you were truly listening during the interview. It’s also just one more way to show your interest and enthusiasm for the job. Sending a thank-you is just good manners.
When should you send one?
Though exact timing varies, most people you would ask would say either the same day or within twenty-four hours. You want the interviewer to be thinking about you and your suitability for the job. Becoming forgettable is never a good thing. This is generally a good time because the interview is still fresh in your mind so you can remember specific things to draw attention to in the thank-you and they still remember who you are.
Handwritten notes are becoming less and less common, so if you really want to stand out, send one by snail mail. However, if you know that the decision is going to be made quickly, send an email. If you really want to send a handwritten note, you can do both. Send an email and a handwritten note so they have double the reminder of you. Just make sure your handwriting looks nice and is legible on the handwritten note.
Other things to keep in mind:
This is business correspondence, so make sure that you read your message. You don’t want to make a fatal error and misspell the company’s name or find it littered with incorrect grammar. If you’re writing a handwritten note, take the time to write it out on a separate piece of paper first so you can edit it as needed before writing it down on the card. To ensure you’re sending the email/note to the right person and right address, make sure to exchange business cards with those you talk with/interview you. Then you’ll know for sure that you’ve got the right information.
Sending a thank-you note after a poor interview probably won’t snag you the job. However, if you did well at the interview, a thank you might just give you that little nudge that will set you above the rest of the crowd. Sweating the small stuff, like thank-yous, is often what sets you apart from the masses.