The Collaborative International Dictionary of English v.0.48:

Post \Post\, v. t. [imp. & p. p. Posted; p. pr. & vb. n.
   Posting.]
   1. To attach to a post, a wall, or other usual place of
      affixing public notices; to placard; as, to post a notice;
      to post playbills.
      [1913 Webster]

   Note: Formerly, a large post was erected before the sheriff's
         office, or in some public place, upon which legal
         notices were displayed. This way of advertisement has
         not entirely gone of use.
         [1913 Webster]

   2. To hold up to public blame or reproach; to advertise
      opprobriously; to denounce by public proclamation; as, to
      post one for cowardice.
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            On pain of being posted to your sorrow
            Fail not, at four, to meet me.        --Granville.
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   3. To enter (a name) on a list, as for service, promotion, or
      the like.
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   4. To assign to a station; to set; to place; as, to post a
      sentinel. "It might be to obtain a ship for a lieutenant,
      . . . or to get him posted." --De Quincey.
      [1913 Webster]

   5. (Bookkeeping) To carry, as an account, from the journal to
      the ledger; as, to post an account; to transfer, as
      accounts, to the ledger.
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            You have not posted your books these ten years.
                                                  --Arbuthnot.
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   6. To place in the care of the post; to mail; as, to post a
      letter.
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   7. To inform; to give the news to; to make (one) acquainted
      with the details of a subject; -- often with up.
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            Thoroughly posted up in the politics and literature
            of the day.                           --Lond. Sat.
                                                  Rev.
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   To post off, to put off; to delay. [Obs.] "Why did I,
      venturously, post off so great a business?" --Baxter.

   To post over, to hurry over. [Obs.] --Fuller.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Posting \Post"ing\, n.
   1. The act of traveling post.
      [1913 Webster]

   2. (Bookkeeping) The act of transferring an account, as from
      the journal to the ledger.
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   Posting house, a post house.
      [1913 Webster]

WordNet (r) 3.0 (2006):

posting
    n 1: a sign posted in a public place as an advertisement; "a
         poster advertised the coming attractions" [syn: poster,
         posting, placard, notice, bill, card]
    2: (bookkeeping) a listing on the company's records; "the
       posting was made in the cash account"
    3: the transmission of a letter; "the postmark indicates the
       time of mailing" [syn: mailing, posting]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "posting":
   allocation, appointment, assignment, booking, cataloging,
   chronicling, collocation, deployment, deposit, deposition,
   designation, disposition, emplacement, enlistment, enrollment,
   entering, entry, impanelment, indexing, inscribing, inscription,
   insertion, inventorying, lading, listing, loading, localization,
   locating, location, logging, matriculation, naming, nomination,
   ordainment, ordination, packing, pinpointing, placement, placing,
   positioning, putting, record keeping, recordation, recording,
   register, registration, registry, reposition, selection, situation,
   spotting, stationing, storage, stowage, tabbing, tabulation,
   transferral



The Jargon File (version 4.4.7, 29 Dec 2003):

posting
 n.

    Noun corresp. to v.: post (but note that post can be nouned).
    Distinguished from a ?letter? or ordinary email message by the fact that
    it is broadcast rather than point-to-point. It is not clear whether
    messages sent to a small mailing list are postings or email; perhaps the
    best dividing line is that if you don't know the names of all the potential
    recipients, it is a posting.


The Free On-line Dictionary of Computing (30 December 2018):

posting

   A message sent to a newsgroup or mailing list (may also be
   called "a post") or the act of sending it.  Distinguished from
   a "letter" or ordinary electronic mail message by the fact
   that it is broadcast rather than point-to-point.  It is not
   clear whether messages sent to a small mailing list are
   postings or e-mail; perhaps the best dividing line is that if
   you don't know the names of all the potential recipients, it
   is a posting.

   [Jargon File]