Message Posting Protocol

Description:  This memo describes a protocol for posting messages from workstations to a mail service host. This RFC specifies an Experimental Protocol for the Internet community.
Author:The Internet Society
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Network Working Group
Request for Comments: 1204
S. Yeh
D. Lee
Netix Communications, Inc.
February 1991

Message Posting Protocol (MPP)

Status of this Memo

This memo describes a protocol for posting messages from workstations (e.g., PCs) to a mail service host. This RFC specifies an Experimental Protocol for the Internet community. Discussion and suggestions for improvement are requested. 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.


Operating systems for personal computers do not provide a mechanism for user authentication. However, such a mechanism is crucial for electronic mail system since authenticating message sender's identity is important in preventing mail forgery. Hence, adding personal computers to an electronic mail network requires an agent (message posting server) to authenticate sender's identity and then submit mail to the message delivery system (e.g., Sendmail, MMDF) on behalf of the sender at a PC. The Netix Message Posting Protocol is developed to be the interface between the message posting server and the PC (client). The protocol is designed to use TCP and is based on the command and reply structures defined for Simple Mail Transfer Protocol (RFC 821) and File Transfer Protocol (RFC 959).


2.1. Command List

USER <SP> <username> <CRLF>
PASS <SP> <password> <CRLF>

2.2. Reply List

220 Message Posting Service Ready.
221 Closing Connection.
250 Command OK.
354 Enter mail, end with <CRLF>.<CRLF>
451 Local error encountered.
500 Command unrecognized.
501 Argument syntax error.
503 Illegal command sequence.
530 Authentication Failure.
550 Error.

2.3. Command and Reply Descriptions

USER <SP> <username> <CRLF>

The USER command informs the message posting server about the username of the user trying to submit mail to the network. The required argument for the USER command is a string specifying the message sender's username.

The USER command can only be used under three conditions:

- when the session with the message posting server has just started;

- right after a message text (terminated by the "<CRLF>.<CRLF>" sequence) has been successfully submitted to the message posting server;

- right after a USER command that gets the reply code 501.

List of possible reply codes for the USER command:

- 250 The username of the message sender has been accepted.

- 451 Internal error has occurred in the message posting server.

- 501 Syntax error detected in the username argument.

- 503 The USER command has been used under an inappropriate condition (i.e., one that is not specified above).

It is recommended that the message posting server should return 250 even if the username is not recognized by the message posting server, as long as the username is syntactically correct. This is an attempt to prevent the message posting server from releasing too much information about the user database. Client should not be able to test the existence of a certain username.

PASS <SP> <password> <CRLF>

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