V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

POP3
       Post Office Protocol 3 (Internet, RFC 1939)


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

POP3

    Version 3 of the Post Office Protocol.
   POP3 is defined in RFC 1081, written in November 1988 by
   Marshall Rose, which is based on RFC 918 (since revised as RFC
   937).  POP3 allows a client computer to retrieve electronic
   mail from a POP3 server via a (temporary) TCP/IP or
   other[?] connection.  It does not provide for sending mail,
   which is assumed to be done via SMTP or some other method.

   POP is useful for computers, e.g. mobile or home computers,
   without a permanent network connection which therefore require
   a "post office" (the POP server) to hold their mail until they
   can retrieve it.

   Although similar in form to the original POP proposed for the
   Internet community, POP3 is similar in spirit to the ideas
   investigated by the MZnet project at the University of
   California, Irvine, and is incompatible with earlier versions
   of POP.

   Substantial work was done on examining POP in a PC-based
   environment.  This work, which resulted in additional
   functionality in this protocol, was performed by the ACIS
   Networking Systems Group at Stanford University.

   RFC 1082 (POP3 Extended Service) extends POP3 to deal with
   accessing mailboxes for mailing lists.

   (1997-01-09)