What is "mail guard"

Mail \Mail\ (m[=a]l), n. [OE. male bag, OF. male, F. malle bag, trunk, mail, OHG. malaha, malha, wallet; akin to D. maal, male; cf. Gael. & Ir. mala, Gr. molgo`s hide, skin.]

1. A bag; a wallet. [Obs.]
   --Chaucer.

2. The bag or bags with the letters, papers, or other matter contained therein, conveyed under public authority from one post office to another; the whole system of appliances used by government in the conveyance and delivery of mail matter.

   There is a mail come in to-day, with letters dated Hague.
   --Tatler.

3. That which comes in the mail; letters, etc., received through the post office.

4. A trunk, box, or bag, in which clothing, etc., may be carried. [Obs.]
   --Sir W. Scott.

   Mail catcher, an iron rod, or other contrivance, attached to a railroad car for catching a mail bag while the train is in motion.

   Mail guard, an officer whose duty it is to guard the public mails. [Eng.]

   Mail train, a railroad train carrying the mail.