As per Relevance of the word provider, we have this rfc below:
Network Working Group R.
Request for Comments: 2645
Category: Standards Track August 1999
ON-DEMAND MAIL RELAY (ODMR
SMTP with Dynamic IP
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
Table of
1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Conventions Used in this Document . . . . . . . . . . . . . . 2
3. Comments . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Description . . . . . . . . . . . . . . . . . . . . . . . . . 2
5. States . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5.1. Initial State . . . . . . . . . . . . . . . . . . . . . . 4
5.1.1. EHLO . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1.2. AUTH . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1.3. QUIT . . . . . . . . . . . . . . . . . . . . . . . . 4
5.2. Authenticated State . . . . . . . . . . . . . . . . . . . 4
5.2.1. ATRN (Authenticated TURN) . . . . . . . . . . . . . 4
5.3. Reversed State . . . . . . . . . . . . . . . . . . . . . 5
5.4. Other Commands . . . . . . . . . . . . . . . . . . . . . 6
6. Example On-Demand Mail Relay Session: . . . . . . . . . . . . 6
7. Response Codes . . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11. Author's Address . . . . . . . . . . . . . . . . . . . . . 8
12. Full Copyright Statement . . . . . . . . . . . . . . . . . . 9
1.
With the spread of low-cost computer systems and
connectivity, the demand for local mail servers has been rising
Many people now want to operate a mail server on a system which
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RFC 2645 On-Demand Mail Relay August 1999
only an intermittent connection to a service provider. If the
has a static IP address, the ESMTP ETRN command [ETRN] can be used
However, systems with dynamic IP addresses (which are very
with low-cost connections) have no widely-deployed solution
This memo proposes a new service, On-Demand Mail Relay (ODMR),
is a profile of SMTP [SMTP, ESMTP], providing for a secure
extensible, easy to implement approach to the problem
2. Conventions Used in this
Because the client and server roles reverse during the session,
avoid confusion, the terms "customer" and "provider" will be used
place of "client" and "server", although of course this protocol
be useful in cases other than commercial service providers
customers
In examples, "P:" is used to indicate lines sent by the provider,
"C:" indicates those sent by the customer. Line breaks within
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].
Examples use 'example.net' as the provider, and 'example.org' and '
example.com' as the customers
3.
Private comments should be sent to the author. Public comments
be sent to the IETF Disconnected SMTP mailing list
. To subscribe, send a message
containing the word SUBSCRIBE
the body
4.
On-Demand Mail Relay is a restricted profile of SMTP [SMTP, ESMTP].
Port 366 is reserved for On-Demand Mail Relay. The initial
and server roles are short-lived, as the point is to allow
intermittently-connected host to request mail held for it by
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 SMTP [SMTP, ESMTP] proceeds
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RFC 2645 On-Demand Mail Relay August 1999
The provider has an On-Demand Mail Relay process listening
connections on the ODMR port. This process does not need to be
full SMTP server. It does need to be an SMTP client with access
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
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).
On-Demand Mail Relay service processes the outgoing queue not on
timer or new mail creation, but on request
The provider side has normal SMTP server responsibilities [SMTP],
including generation of delivery failure notices, etc. as needed
5.
The On-Demand Mail Relay service has three states: an initial state
an authenticated state, and a reversed state. The state
is illustrated in the following diagram
---------------------------
! initial state !
---------------------------
! !
QUIT
! !
!
! -----------------------
! ! authenticated state !
! -----------------------
! ! !
! QUIT
! ! !
! !
! ! ------------------
! ! ! reversed state !
! ! ------------------
! ! !
! !
! ! !
V V
---------------------
! termination !
---------------------
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RFC 2645 On-Demand Mail Relay August 1999
(Note that in the reversed state, commands are sent by the provider
not the customer.)
5.1. Initial
In the initial state, the provider is the server and the customer
the client. Three commands are valid: EHLO, AUTH, and QUIT
5.1.1.
The EHLO command is the same as in [ESMTP]. The response
include AUTH and ATRN
5.1.2.
The AUTH command is specified in [AUTH]. The AUTH command uses
[SASL] mechanism to authenticate the session. The session is
considered authenticated until a success response to AUTH has
sent
For interoperability, implementations MUST support the CRAM-MD
mechanism [CRAM]. Other SASL mechanisms may be supported. A
MAY disable CRAM-MD5 support if it uses more secure methods.
EXTERNAL mechanism [SASL] might be useful in some cases, for example
if the provider has already authenticated the client, such as
a PPP connection
5.1.3.
The QUIT command is the same as in [SMTP].
5.2. Authenticated
The authenticated state is entered after a successful AUTH command
Two commands are valid in the authenticated state: ATRN and QUIT
5.2.1. ATRN (Authenticated TURN
Unlike the TURN command in [SMTP], the ATRN command optionally
one or more domains as a parameter. The ATRN command MUST
rejected if the session has not been authenticated. Response
530 [AUTH] is used for this
The timeout for this command MUST be at least 10 minutes to allow
provider time to process its mail queue
An ATRN command sent with no domains is equivalent to an ATRN
specifying all domains to which the customer has access
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RFC 2645 On-Demand Mail Relay August 1999
If the authentication used by the customer does not provide access
all of the domains specified in ATRN, the provider MUST NOT send
for any domains to the customer; the provider MUST reject the
command with a 450 code
If the customer does have access to all of the specified domains,
none of them have any queued mail, the provider normally rejects
ATRN command with response code 453. The provider MAY instead
a 250 success code, and after the roles are reversed, send a
following the EHLO
The provider MAY also reject the ATRN command with a 450 response
indicate refusal to accept multiple requests issued within
particular time interval
If the customer has access to all of the specified domains and
exists in at least one of them, the provider issues a 250
code
If the server is unable to verify access to the requested
(for example, a mapping database is temporarily unavailable),
response code 451 is sent
[ABNF] for ATRN
atrn = "ATRN" [SP domain *("," domain)]
domain = sub-domain 1*("." sub-domain
sub-domain = (ALPHA / DIGIT) *(ldh-str
ldh-str = *(ALPHA / DIGIT / "-") (ALPHA / DIGIT
5.3. Reversed
After the provider has sent a success reply to the ATRN command,
roles reverse, and the customer becomes the server, and the
becomes the client
After receiving the success response to ATRN, the customer sends
standard SMTP initial greeting line. At this point normal
[SMTP, ESMTP] commands are used. Typically the provider sends
after seeing the customer's greeting, to be followed by MAIL FROM
so on
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RFC 2645 On-Demand Mail Relay August 1999
5.4. Other
The provider MAY reject all commands other than EHLO, AUTH, ATRN,
QUIT with response code 502.
6. Example On-Demand Mail Relay
P: 220 EXAMPLE.NET on-demand mail relay server
C: EHLO example.
P: 250-EXAMPLE.
P: 250-AUTH CRAM-MD5
P: 250
C: AUTH CRAM-MD
P: 334 MTg5Ni42OTcxNzA5NTJASVNQLkNPTQo
C: Zm9vYmFyLm5ldCBiOTEzYTYwMmM3ZWRhN2E0OTViNGU2ZTczMzRkMzg5MAo
P: 235 now authenticated as example.
C: ATRN example.org,example.
P: 250 OK now reversing the
C: 220 example.org ready to receive
P: EHLO EXAMPLE.
C: 250-example.
C: 250
P: MAIL FROM:
C: 250
P: RCPT TO:
C: 250 OK, recipient
...
P:
C: 221 example.org closing
7. Response
The response codes used in this document are
250 Requested mail action okay,
450 ATRN request
451 Unable to process ATRN request
453 You have no
502 Command not
530 Authentication required [AUTH
8. Security
Because access to the On-Demand Mail Relay server is only useful
a prior arrangement between the parties (so the provider is
target of MX records for the customer's domains and thus has mail
relay), it may be useful for the provider to restrict access to
On-Demand Mail Relay port. For example, the ODMR server could
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RFC 2645 On-Demand Mail Relay August 1999
configurable, or a TCP wrapper or firewall could be used, to
access to port 366 except within the provider's network. This
be useful when the provider is the customer's ISP. Use of
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
secure authentication mechanisms in the future
See sections 5.1.2 and 5.2.1 for additional security details
9.
This memo has been developed in part based on comments
discussions which took place on and off the IETF-disconn-smtp
list. Special thanks to Chris Newman and Ned Freed for
comments
10.
[ABNF] Crocker, D. and P. Overell, "Augmented BNF for
Specifications: ABNF", RFC 2234, November 1997.
[AUTH] Myers, J., "SMTP Service Extension for Authentication",
RFC 2554, March 1999.
[CRAM] Klensin, J., Catoe, R. and P. Krumviede, "IMAP/
AUTHorize Extension for Simple Challenge/Response",
2195, September 1997.
[ESMTP] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D
Crocker, "SMTP Service Extensions", RFC 1869,
1995.
[ETRN] De Winter, J., "SMTP Service Extension for Remote
Queue Starting", RFC 1985, August 1996.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SASL] Myers, J., "Simple Authentication and Security
(SASL)", RFC 2222, October 1997.
[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10,
821, August 1982.
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RFC 2645 On-Demand Mail Relay August 1999
11. Author's
Randall
QUALCOMM
5775 Morehouse Dr
San Diego, CA 92121-2779
U.S.A
Phone: +1.619.651.5115
EMail: randy@qualcomm.
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RFC 2645 On-Demand Mail Relay August 1999
12. Full Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Gellens Standards Track [Page 9]
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