mail (n.1) Look up mail at Dictionary.com
"post, letters," c.1200, "a traveling bag," from Old French male "wallet, bag, bundle," from Frankish *malha or some other Germanic source, from Proto-Germanic *malho- (cognates: Old High German malaha "wallet, bag," Middle Dutch male "bag"), from PIE *molko- "skin, bag." Sense extension to "letters and parcels" (18c.) is via "bag full of letter" (1650s) or "person or vehicle who carries postal matter" (1650s). In 19c. England, mail was letters going abroad, while home dispatches were post. Sense of "personal batch of letters" is from 1844, originally American English.
mail (n.2) Look up mail at Dictionary.com
"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.
mail (v.) Look up mail at Dictionary.com
"send by post," 1828, American English, from mail (n.1). Related: Mailed; mailing; mailable. Mailing list attested from 1876.
mail (n.3) Look up mail at Dictionary.com
"rent, payment," from Old English mal (see blackmail (n.)).