The Collaborative International Dictionary of English v.0.48:

Mail \Mail\, n. [F. maille, OF. also maaille, LL. medalia. See
   Medal.]
   1. A small piece of money; especially, an English silver
      half-penny of the time of Henry V. [Obs.] [Written also
      maile, and maille.]
      [1913 Webster]

   2. Rent; tribute. [Obs., except in certain compounds and
      phrases, as blackmail, mails and duties, etc.]
      [1913 Webster]

   Mail and duties (Scots Law), the rents of an estate, in
      whatever form paid.
      [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

MAILE, ancient English law. A small piece of money; it also signified a
rent, because the rent was paid with maile.