1. Introduction

   On certain types of smaller nodes in the Internet it is often
   impractical to maintain a message transport system (MTS).  For
   example, a workstation may not have sufficient resources (cycles,
   disk space) in order to permit a SMTP server [RFC821] and associated
   local mail delivery system to be kept resident and continuously
   running.  Similarly, it may be expensive (or impossible) to keep a
   personal computer interconnected to an IP-style network for long
   amounts of time (the node is lacking the resource known as
   "connectivity").

   Despite this, it is often very useful to be able to manage mail on
   these smaller nodes, and they often support a user agent (UA) to aid
   the tasks of mail handling.  To solve this problem, a node which can
   support an MTS entity offers a maildrop service to these less endowed
   nodes.  The Post Office Protocol - Version 3 (POP3) is intended to
   permit a workstation to dynamically access a maildrop on a server
   host in a useful fashion.  Usually, this means that the POP3 is used
   to allow a workstation to retrieve mail that the server is holding
   for it.

   For the remainder of this memo, the term "client host" refers to a
   host making use of the POP3 service, while the term "server host"
   refers to a host which offers the POP3 service.