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Post Office Protocol: Version 3 (RFC1225) Disclosure Number: IPCOM000002039D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2019-Feb-11
Document File: 16 page(s) / 20K

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Internet Society Requests For Comment (RFCs)

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10.17487/RFC1225: DOI


This memo suggests a simple method for workstations to dynamically access mail from a mailbox server. [STANDARDS-TRACK]

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 9% of the total text.

Network Working Group M. Rose Request for Comments: 1225 Performance Systems International Obsoletes: RFC 1081 May 1991

Post Office Protocol - Version 3

Status of this Memo

This memo suggests a simple method for workstations to dynamically access mail from a mailbox server. This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited.


This memo is a republication of RFC 1081 which was based on RFC 918 (since revised as RFC 937). Although similar in form to the original Post Office Protocol (POP) proposed for the Internet community, the protocol discussed in this memo is similar in spirit to the ideas investigated by the MZnet project at the University of California, Irvine.

Further, 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. The author gratefully acknowledges their interest.


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 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

Rose [Page 1]

RFC 1225 POP3 May 1991

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.

A Short Digression

This memo does not specify how a client host enters mail into the transport system, although a method consistent with the philosophy of this memo is presented here:

When the user agent on a client host wishes to enter a message into the transport system, it establishes an SMTP connection to its relay host (this relay host could be, but need not be, the POP3 server host for the client host).

If this method is followed, then the client host appears to th...