Yes, you really do have to send a thank-you note after a job interview—here's why

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Yes, you need to send a thank-you note after a job interview.

This might be unwelcome news, especially if you sided against the somewhat old-fashioned practice at the center of the recent, highly contentious online debate surrounding an article by Business Insider executive managing editor Jessica Liebman. In a post for Business Insider, Liebman wrote that when she first started hiring, she came up with "a simple rule: We shouldn't move a candidate to the next stage in the interview process unless they send a thank-you email."

Plenty of people disagreed with Liebman, but her stance gets at the very heart of why it is always better as a job seeker to err on the side of caution and send a thank-you note: You never know what the hiring manager may consider a deal-breaker.

While not all hiring managers take thank-you notes as seriously as Liebman, 80% find such messages helpful when reviewing candidates, according to a survey by Accountemps.

But only a fourth of hiring managers ever actually receive thank-you notes from applicants, meaning taking 10 minutes to compose such a note to the HR manager or employer who interviewed you is one of the easiest things you can do to set yourself apart — in the best way — from other applicants.

"I believe applicants should still send thank-you notes," Alicia M. King, director of talent management and inclusion for the Society for Human Resource Managers tells CNBC Make It. "HR managers and the interview team do actually read them and it shows that a candidate is truly invested in the role and interested in working for the company."

Liebman (who clarified in a follow-up article that her stance is a rule of thumb and not an official policy) writes that not sending a thank you is the No. 1 mistake job seekers can make, because it signals an applicant probably doesn't want the job, and she will likely be ghosted or rejected if she makes an offer. Those who do send one, on the other hand, appear eager, organized, well-manned and resourceful — or, as she wrote, like "good eggs."

Critics on social media argued that using thank-you notes as a way of culling applicants can reinforce culturally homogeneous office norms, and doesn't actually correlate to job performance. Others saw no need to thank a company for what is essentially a mutually beneficial exchange: The organization needs talented employees to fill its needs, and job seekers want a fulfilling job that pays a decent wage.

But until hiring managers stop using these messages in their deliberations about candidates, or all workers agree to entirely forgo the practice, you should send one.

What to say in your note

Think of your message as an opportunity to follow up with an employer and make a final sales pitch for yourself, reminding them once again about your talents and why you're best-suited to fill the role. The key to successfully doing that: customization.

"Each thank-you note should be customized to the receiver. It shouldn't be generic," says King. "It won't resonate if you haven't taken the time to reflect on the interview."

Try mentioning something exciting you learned about the company that makes you want to work there, a skills shortage you now know they have that you're uniquely poised to fill, or extra talents or experiences you didn't get to share during the interview. Include links to projects or work samples you mentioned in the course of your conversation. Or, if you stumbled on a question during the interview, work the answer you wish you'd given into the note.

Another trick King recommends: asking the hiring manager at the end of the interview if there is anything hanging them up about hiring you.

"Learn what's giving them pause and then you can address that while in the interview and in your thank-you note," says King. "You would be surprised how many managers will give some feedback when directly asked. It likely won't be an in-depth answer, but they may say we're looking for someone who has this certain skill, and then you can address that in your note with examples demonstrating that skill."

Avoid common mistakes

Incorporating these small details will show a manager that you're thoughtful, a careful listener and well-suited for the gig. If you interview with multiple people at an organization, it should also save you the embarrassment of having managers compare your letters and realize they're all identical.

And make sure you've got the manager and company name right. "It's one of the biggest mistakes I see. If you're going to reuse the same thank-you note, make sure you, at least, change the person's name," says King.

Finally, you need to get all that information into a couple short paragraphs.

"Your thank-you note should be concise, no more than a page," says King. "Think of it as a memo you would write someone at work."

When and how to send your note

There is a sweet spot for timing when you send your message. You don't want it to arrive too soon or too late, which is why King says you need to send it within the 24-to 48-hour-period after an interview.

"You don't want to send it too quickly and the manager to feel like it is generic or was drafted before the interview. It's really important to take some time and reflect on the interview and what was discussed so you can add elements from the conversation into your thank-you note," says King. "Wait too long to send it and the manager is going to think you're not eager or really interested in the role. The note won't have the same meaning."

No matter the kind of interview, be it in-person or via the phone or Skype, send a thank-you note following up with each person you met. And if you have multiple interviews with the same company, send new notes following each round.

"This is why customizing and tailoring is important. You don't want to be sending the same note every time," says King.

Almost all, 94%, of HR managers say it's appropriate to send a thank-you note via email, according to that same Accountemps survey.

Occasionally, you may need to go old-school and snail-mail it. But that largely depends on the culture of the place you're applying to, how formal and traditional it is, and how you've corresponded in the past. If they've emailed you, you're fine emailing. If they reached out by phone or mail, consider putting yours in the post. (It doesn't need to be handwritten either, typed is fine, especially if you've got poor penmanship.)

However you chose to send your note, it is important that you only send one to each person following each interview round.

"One person I interviewed sent me a personalized thank-you letter, then sent a thank-you email and then sent a portfolio. It felt borderline desperate," says King. You don't want to overwhelm or inundate your interviewer.

If you don't hear back from a company in the two-week period after you've sent your thank-you note, then you can reach out again and ask for any news or updates.

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