One document matched: draft-gellens-on-demand-04.txt
Differences from draft-gellens-on-demand-03.txt
Document: draft-gellens-on-demand-04.txt QUALCOMM
Expires: 17 December 1998 17 June 1998
On-Demand Mail Relay
Status of this Memo:
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a
"working draft" or "work in progress."
To learn the current status of any Internet Draft, please check the
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ftp.isi.edu (US West Coast).
A version of this draft document is intended for submission to the
RFC editor as a Proposed Standard for the Internet Community.
Discussion and suggestions for improvement are requested. Please
send comments to the IETF Disconnected SMTP mailing list,
<ietf-disconn-smtp@imc.org>. To subscribe, send a message containing
SUBSCRIBE to <ietf-disconn-smtp-request@imc.org>.
Copyright Notice
Copyright (C) The Internet Society 1998. All Rights Reserved.
Introduction
With the spread of low-cost computer systems and Internet
connectivity, the demand for local mail servers had been rising.
Many people now want to operate a mail server on a system which has
only an intermittent connection to a service provider. If the
system has a static IP address, the [ESMTP] [ETRN] command can be
used. However, systems with dynamic IP addresses (which are very
common with low-cost connections) have no widely-deployed solution.
This memo proposes a new service, On-Demand Mail Relay, which is a
profile of [ESMTP], providing for a secure, extensible, easy to
implement approach to the problem.
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1. Conventions Used in this Document
Because the client and server roles reverse during the session, to
avoid confusion, the terms "customer" and "provider" will be used in
place of "client" and "server", although of course this protocol may
be useful in cases other than commercial service providers and
customers.
In examples, "P:" is used to indicate lines sent by the provider,
and "C:" indicates those sent by the customer. Line breaks within a
command are for editorial purposes only.
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
in this document are to be interpreted as defined in [KEYWORDS].
2. Description
On-Demand Mail Relay is a restricted profile of SMTP which runs on
port 366. The initial client and server roles are short-lived, as
the point is to allow the intermittently-connected host to request
mail held for it by a service provider.
The customer initiates a connection to the provider, authenticates,
and requests its mail. The roles of client and server then reverse,
and normal [ESMTP] proceeds.
The provider has an On-Demand Mail Relay process listening for
connections on port 366. This process does not need to be a full
SMTP server. It does need to be an SMTP client with access to the
outgoing mail queues, and as a server implement the EHLO, AUTH,
ATRN, and QUIT commands.
An MTA normally has a mail client component which processes the
outgoing mail queues, attempting to send mail for particular
domains, based on time or event (such as new mail being placed in
the queue, or receipt of an ETRN command by the SMTP server
component). The On-Demand Mail Relay service processes the outgoing
queue not on a timer or new mail creation, but on request.
The provider side has normal SMTP server responsibilities, including
generation of relay or failure DSNs as needed.
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3. States
The On-Demand Mail Relay service has three states: an initial state,
an authenticated state, and a reversed state. The state progression
is illustrated in the following diagram:
---------------------------
! initial state !
---------------------------
! !
QUIT AUTH
! !
! V
! -----------------------
! ! authenticated state !
! -----------------------
! ! !
! QUIT ATRN
! ! !
! ! V
! ! ------------------
! ! ! reversed state !
! ! ------------------
! ! !
! ! QUIT
! ! !
V V V
---------------------
! termination !
---------------------
3.1. Initial State
In the initial state, the provider is the server and the customer is
the client. Three commands are valid: EHLO, AUTH, and QUIT.
3.1.1. EHLO
The EHLO command is the same as in [ESMTP]. The response must
include AUTH and ATRN.
3.1.2. AUTH
The AUTH command is specified in [AUTH]. The AUTH command uses a
[SASL] mechanism to authenticate the session. The session is not
considered authenticated until a success response to AUTH has been
sent.
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For interoperability, implementations MUST support the CRAM-MD5
mechanism [CRAM]. Other SASL mechanisms may be supported. A site
MAY disable CRAM-MD5 support if it uses more secure methods. The
EXTERNAL mechanism [SASL] might be useful in some cases, for
example, if the provider has already authenticated the client, such
as during a PPP connection.
3.1.3. QUIT
The QUIT command is the same as in [SMTP].
3.2. Authenticated State
The authenticated state is entered after a successful AUTH command.
Two commands are valid in the authenticated state: ATRN and QUIT.
3.2.1. ATRN (Authenticated TURN)
Unlike the TURN command in [SMTP], the ATRN command optionally takes
one or more domains as a parameter. The ATRN command MUST be
rejected if the session has not been authenticated. Response code
505 should be used for this.
The timeout for this command MUST be at least 10 minutes to allow
the provider time to process its mail queue.
An ATRN command sent with no domains is equivalent to an ATRN
command specifying all domains to which the customer has access.
If the authentication used by the customer does not provide access
to all of the domains specified in ATRN, the provider MUST NOT send
mail for those domains to the customer; the provider MUST reject the
ATRN command with a 450 code.
If the customer does have access to all of the specified domains,
but none of them have any queued mail, the provider normally rejects
the ATRN command with response code 453. The provider MAY use
response code 450, to avoid disclosing information to unauthorized
parties regarding the domains for which it provides ODMR service.
Or, the provider MAY issue a 250 success code, and after the roles
are reversed, send a QUIT following the EHLO.
The provider MAY also reject the ATRN command with a 450 response to
indicate refusal to accept multiple requests issued within a
particular time interval.
If the customer has access to all of the specified domains and mail
exists in at least one of them, the provider issues a 250 success
code.
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If the server is unable to verify access to the requested domains
(for example, a mapping database is temporarily unavailable),
response code 451 is sent.
[ABNF] for ATRN:
atrn = "ATRN" [domain *("," domain)]
domain = sub-domain 1*("." sub-domain)
sub-domain = (ALPHA / DIGIT) *(ldh-str)
ldh-str = *(ALPHA / DIGIT / "-") (ALPHA / DIGIT)
3.3. Reversed State
After the provider has sent a success reply to the ATRN command, the
roles reverse, and the customer becomes the server, and the provider
becomes the client. At this point normal [ESMTP] commands are used.
Typically the provider sends EHLO immediately following the success
response to ATRN, to be followed by MAIL FROM and so on.
3.4. Other Commands
The provider MAY reject all commands other than EHLO, AUTH, ATRN,
and QUIT with response code 502.
4. Example On-Demand Mail Relay Session:
P: 220 ISP.NET on-demand mail relay server ready
C: EHLO foobar.net
P: 250-AUTH CRAM-MD5 Kerberos-v5
P: 250 ATRN
C: AUTH CRAM-MD5
P: 334 MTg5Ni42OTcxNzA5NTJASVNQLkNPTQo=
C: Zm9vYmFyLm5ldCBiOTEzYTYwMmM3ZWRhN2E0OTViNGU2ZTczMzRkMzg5MAo=
P: 235 now authenticated as foobar.net
C: ATRN foobar.net, vanity.com
P: 250 OK now reversing the connection
P: EHLO ISP.NET
C: 250 SIZE
P: MAIL FROM: <Lester.Tester@dot.foo.org>
C: 250 OK
P: RCPT TO: <l.eva.msg@vanity.com>
C: 250 OK, recipient accepted
...
P: QUIT
C: 221 foobar.net closing connection
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5. Response Codes
The response codes used in this document are:
250 Requested mail action okay, completed
450 ATRN request refused
451 Unable to process ATRN request now
453 You have no mail
502 Command not implemented
505 Authentication required
6. Security Considerations
Because access to the On-Demand Mail Relay server is only useful
with a prior arrangement between the parties (so the provider is the
target of MX records for the customer's domains and thus has mail to
relay), it may be useful for the provider to restrict access to the
On-Demand Mail Relay port. For example, a TCP wrapper or firewall
could be used to block access to port 366 except within the
provider's network. This might be useful when the provider is the
customer's ISP. Use of such mechanisms does not reduce the need for
the AUTH command, however, but can increase the security it
provides.
Use of SASL in the AUTH command allows for substitution of more
secure authentication mechanisms in the future.
See sections 3.1.2 and 3.2.1 for additional security details.
7. Acknowledgments
This draft has been developed in part based on comments and
discussions which took place on and off the IETF-disconn-smtp
mailing list. Special thanks to Chris Newman and Ned Freed for
their comments.
8. References
[ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd.,
November 1997. <ftp://ftp.isi.edu/in-notes/rfc2234.txt>
[AUTH] Myers, J., "SMTP Service Extension for Authentication", (work
in progress),
<ftp://ftp.isi.edu/internet-drafts/draft-myers-smtp-auth-11.txt>
[CODES-EXTENSION] Freed, N., "SMTP Service Extension for Returning
Enhanced Error Codes", RFC 2034, October 1996,
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<ftp://ftp.isi.edu/in-notes/rfc2034.txt>
[CRAM] Klensin, J., Catoe, R., Krumviede, P. "IMAP/POP AUTHorize
Extension for Simple Challenge/Response", RFC 2195, September 1997,
<ftp://ftp.isi.edu/in-notes/rfc2195.txt>
[ESMTP] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extensions", RFC 1869, STD 10, November 1995,
<ftp://ftp.isi.edu/in-notes/rfc1869.txt>
[ETRN] De Winter, J., "SMTP Service Extension for Remote Message
Queue Starting", RFC 1985, August 1996,
<ftp://ftp.isi.edu/in-notes/rfc1985.txt>
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997,
<ftp://ftp.isi.edu/in-notes/rfc2119.txt>
[SASL] Myers, J., "Simple Authentication and Security Layer (SASL)",
RFC 2222, October 1997, <ftp://ftp.isi.edu/in-notes/rfc2222.txt>
[SMTP-CODES] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC
1893, January 1996, <ftp://ftp.isi.edu/in-notes/rfc1893.txt>
[SMTP] J. Postel, "Simple Mail Transfer Protocol", RFC 821, STD 10,
August 1982, <ftp://ftp.isi.edu/in-notes/rfc821.txt>
9. Full Copyright Statement
Copyright (C) The Internet Society 1998. All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
10. Author's Address
Randall Gellens +1.619.651.5115
Qualcomm, Inc. +1.619.651.5334 (fax)
6455 Lusk Blvd. Randy@Qualcomm.Com
San Diego, CA 92121-2779
U.S.A.
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