The executive managing editor of Insider Inc. has hired hundreds of people over 10 years.

She uses an easy test to see whether a candidate really wants the job and is a "good egg": Did they send a thank-you email?

If not, don't hire them. You'll probably regret it.

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Making someone an offer to join your company is always risky.

The truth is, the hiring process can uncover only so much. You're often basing your decision on a small sample of data that you collected during a few hours of speaking with them, sometimes not even in person.

Sure, maybe you had them take a test or complete an exercise, and you talked to three people who worked with them previously. But still, you never really know how it's going to work out until they come on board. And sometimes even the most promising hires turn out to be the wrong fit.

As the executive managing editor of Insider Inc., I interview people all the time for open jobs. I have hired hundreds of them.

When I first started hiring, I 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.

I wrote a piece in 2012 that explained the No. 1 mistake that people I interviewed were making: not sending thank-you emails. Many people disagreed with me. I received lots of angry emails.

Still, seven years later, I stand by it.

(To be clear, I am not speaking about handwritten, snail-mail thank-you notes. As I wrote back then, you should never send a handwritten thank-you note. That still stands.)

As a hiring manager, you should always expect a thank-you email, and you should never make an offer to someone who neglected to send one.

Why?

The thank-you email reflects two important things:

It signals that the person wants the job — or rather, no thank-you email signals the person probably doesn't want the job. The handful of times we've moved forward with a candidate despite not receiving a thank you, we've been ghosted, or the offer we make is ultimately rejected. A few times, the offer is accepted, but the person pulls out before their start date or leaves after a few months. How someone presents in interviews might not translate to effectiveness in the role. While sending a thank-you note doesn't necessarily guarantee the person will be a good hire, it gives you the tiniest bit more data: The candidate is eager, organized, and well mannered enough to send the note. It shows resourcefulness, too, because the candidate often has to hunt down an email address the interviewer never gave them. At Insider Inc., we look to hire "good eggs." The thank-you email is a mark for the good-egg column.

To be clear, a thank-you note does not ensure someone will be a successful hire. But using the thank-you email as a barrier to entry has proved beneficial, at least at my company.

Update: After this story went viral with tons of readers agreeing and disagreeing vehemently with my rule of thumb, I posted a follow-up article to clarify my thoughts.