SMTP Service Extension for Remote Message Queue Starting (RFC1985)
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2019-Feb-14
Internet Society Requests For Comment (RFCs)
This memo defines an extension to the SMTP service whereby an SMTP client and server may interact to give the server an opportunity to start the processing of its queues for messages to go to a given host. [STANDARDS-TRACK]
Network Working Group J. De Winter Request for Comments: 1985 Wildbear Consulting, Inc. Category: Standards Track August 1996
SMTP Service Extension for Remote Message Queue Starting
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
This memo defines an extension to the SMTP service whereby an SMTP client and server may interact to give the server an opportunity to start the processing of its queues for messages to go to a given host. This extension is meant to be used in startup conditions as well as for mail nodes that have transient connections to their service providers.
The TURN command was a valid attempt to address the problem of having to start the processing for the mail queue on a remote machine. However, the TURN command presents a large security loophole. As there is no verification of the remote host name, the TURN command could be used by a rogue system to download the mail for a site other than itself.
Therefore, this memo introduces the ETRN command. This command uses the mechanism defined in  to define extensions to the SMTP service whereby a client ("sender-SMTP") may request that the server ("receiver-SMTP") start the processing of its mail queues for messages that are waiting at the server for the client machine. If any messages are at the server for the client, then the server should create a new SMTP session and send the messages at that time.
De Winter Standards Track [Page 1]
RFC 1985 SMTP Service Extension - ETRN August 1996
2. Framework for the ETRN Extension
The following service extension is therefore defined:
(1) the name of the SMTP service extension is "Remote Queue Processing Declaration";
(2) the EHLO keyword value associated with this extension is "ETRN", with no associated parameters;
(3) one additional verb, ETRN, with a single parameter that specifies the name of the client(s) to start processing for;
(4) no additional SMTP verbs are defined by this extension.
The remainder of this memo specifies how support for the extension affects the behavior of an SMTP client and server.
3. The Remote Queue Processing Declaration service extension
To save money, many small companies want to only maintain transient connections to their service providers. In addition, there are some situations where the client sites depend on their mail arriving quickly, so forcing the queues on the server belonging to their service provider may be more desirable than waiting for the retry timeout to occur.
Both of these situations could currently be fixed using the TURN command defined in , if it were not for a large security loophole in the TURN command. As it stands, the TURN command will reverse the di...