"having mail armor," late 14c., from mail (n.2). Of animals having protective skin or scales, by 1680s.
Entries linking to mailed
mail n.2
"metal ring armor," c. 1300, from Old French maille "link of mail, mesh of net," from Latin macula "mesh in a net," originally "spot, blemish," on notion that the gaps in a net or mesh looked like spots. Its use dates from late Roman times. The favorite armor in Europe 12c.-13c., it was effective, but heavy and costly.