SMTP Service Extensions
RFC 1869
Document | Type |
RFC - Internet Standard
(November 1995; No errata)
Obsoleted by RFC 2821
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Authors | Dave Crocker , John Klensin , Einar Stefferud , Marshall Rose , Ned Freed | ||
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 1869 (Internet Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group J. Klensin, WG Chair Request For Comments: 1869 MCI STD: 10 N. Freed, Editor Obsoletes: 1651 Innosoft International, Inc. Category: Standards Track M. Rose Dover Beach Consulting, Inc. E. Stefferud Network Management Associates, Inc. D. Crocker Brandenburg Consulting November 1995 SMTP Service Extensions 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. 1. Abstract This memo defines a framework for extending the SMTP service by defining a means whereby a server SMTP can inform a client SMTP as to the service extensions it supports. Extensions to the SMTP service are registered with the IANA. This framework does not require modification of existing SMTP clients or servers unless the features of the service extensions are to be requested or provided. 2. Introduction The Simple Mail Transfer Protocol (SMTP) [1] has provided a stable, effective basis for the relay function of message transfer agents. Although a decade old, SMTP has proven remarkably resilient. Nevertheless, the need for a number of protocol extensions has become evident. Rather than describing these extensions as separate and haphazard entities, this document enhances SMTP in a straightforward fashion that provides a framework in which all future extensions can be built in a single consistent way. 3. Framework for SMTP Extensions For the purpose of service extensions to SMTP, SMTP relays a mail object containing an envelope and a content. Klensin, et al Standards Track [Page 1] RFC 1869 SMTP Service Extensions November 1995 (1) The SMTP envelope is straightforward, and is sent as a series of SMTP protocol units: it consists of an originator address (to which error reports should be directed); a delivery mode (e.g., deliver to recipient mailboxes); and, one or more recipient addresses. (2) The SMTP content is sent in the SMTP DATA protocol unit and has two parts: the headers and the body. The headers form a collection of field/value pairs structured according to RFC 822 [2], whilst the body, if structured, is defined according to MIME [3]. The content is textual in nature, expressed using the US ASCII repertoire (ANSI X3.4-1986). Although extensions (such as MIME) may relax this restriction for the content body, the content headers are always encoded using the US ASCII repertoire. The algorithm defined in [4] is used to represent header values outside the US ASCII repertoire, whilst still encoding them using the US ASCII repertoire. Although SMTP is widely and robustly deployed, some parts of the Internet community might wish to extend the SMTP service. This memo defines a means whereby both an extended SMTP client and server may recognize each other as such and the server can inform the client as to the service extensions that it supports. It must be emphasized that any extension to the SMTP service should not be considered lightly. SMTP's strength comes primarily from its simplicity. Experience with many protocols has shown that: protocols with few options tend towards ubiquity, whilst protocols with many options tend towards obscurity. This means that each and every extension, regardless of its benefits, must be carefully scrutinized with respect to its implementation, deployment, and interoperability costs. In many cases, the cost of extending the SMTP service will likely outweigh the benefit. Given this environment, the framework for the extensions described in this memo consists of: (1) a new SMTP command (section 4) (2) a registry of SMTP service extensions (section 5) (3) additional parameters to the SMTP MAIL FROM and RCPT TO commands (section 6). Klensin, et al Standards Track [Page 2] RFC 1869 SMTP Service Extensions November 1995 4. The EHLO command A client SMTP supporting SMTP service extensions should start an SMTPShow full document text