Only 24 percent of job candidates send a thank-you email after an interview.

Meanwhile, 80 percent of hiring managers say a thank-you note influences their evaluation, and 68 percent say it directly affects their hiring decision.

That gap is the largest free advantage in modern job searching. A 100-word email that takes 10 minutes to write changes how a hiring manager thinks about you. Most candidates skip it entirely. The ones who send it move themselves forward in a way the others cannot.

Here's how to actually write one that works.

What a thank-you email is actually for