1. Introduction
For certain types of smaller nodes in the Internet, it is impractical to maintain a Message Transport System (MTS). For example, a workstation may not have sufficient resources (cycles, disk space) to permit an 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 network for long amounts of time, given the possibility of PPP dial-up connections being the only available connectivity for such a node.
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 protocol is used to allow a workstation to retrieve mail that the server is holding for it.
POP3 is not intended to provide extensive manipulation of messages on the server; normally, mail is downloaded and then deleted. A more advanced (and complex) protocol, IMAP4, is discussed in [RFC1730].
For the remainder of this memo, the term "client host" refers to a host using the POP3 service, while the term "server host" refers to a host which offers the POP3 service.
Glossary:
- MTS (Message Transport System): The system responsible for mail transport
- UA (User Agent): Mail handling software
- maildrop: A mailbox on a server
- client host: A host using the POP3 service
- server host: A host offering the POP3 service