Knight's armor

I believe the answer is:

mail

(Other definitions for mail that I've seen before include "protective cover" , "Eg, letters" , "Armour; posted items" , "letter?" , "some self-defence material" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.