The Collaborative International Dictionary of English v.0.48:

Mail \Mail\, v. t. [imp. & p. p. Mailed; p. pr. & vb. n.
   Mailing.]
   To deliver into the custody of the postoffice officials, or
   place in a government letter box, for transmission by mail;
   to post; as, to mail a letter. [U. S.]
   [1913 Webster]

   Note: In the United States to mail and to post are both in
         common use; as, to mail or post a letter. In England
         post is the commoner usage.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Mailing \Mail"ing\, n. [Scot., fr. mail tribute, rent. See 2d
   Mail.]
   A farm. [Scot.] --Sir W. Scott.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

mailing \mail"ing\, n.
   1. The act or process of sending materials through the mail.
      [PJC]

   2. A quantity of mail, such as letters, magazines,
      advertising brochures, etc., sent at one time by one
      person or organization; as, the ads with coupons will go
      out in our next mailing.
      [PJC]

WordNet (r) 3.0 (2006):

mailing
    n 1: mail sent by a sender at one time; "the candidate sent out
         three large mailings"
    2: the transmission of a letter; "the postmark indicates the
       time of mailing" [syn: mailing, posting]