Internet DRAFT - draft-ietf-lemonade-futuredelivery
draft-ietf-lemonade-futuredelivery
INTERNET-DRAFT G. White
draft-ietf-lemonade-futuredelivery-04.txt Independent
Updates: RFC 3463, 3464 G. Vaudreuil
Expires: September 9, 2006 Lucent Technologies
March 9, 2006
SMTP Submission Service Extension for Future Message Release
Status of this Memo
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Abstract
This memo defines an extension to the SMTP submission protocol for a
client to indicate a future time for the message to be released for
delivery. This extension permits a client to use server-based
storage for a message that should be held in queue until an
appointed time in the future. This is useful for clients which do
not have local storage or are otherwise unable to release a message
for delivery at an appointed time.
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1. Introduction
There is a widely-used feature within the voice messaging community
to compose and send a message for delivery in the future. This is
useful for sending announcements to be heard at the beginning of a
work day, to send birthday greetings a day or so ahead, or to use as
a lightweight facility to build a personal reminder service.
This extension uses the SMTP submission protocol [n3] to allow a
client, when submitting a message, to indicate a future time for the
message to be released for delivery.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [n1].
3. Framework
The Future Message Release service extension for SMTP submission uses
the SMTP service extension mechanism [n4] to extend the SMTP
submission protocol [n3]. The following SMTP submission service
extension is hereby defined:
The name of the SMTP submission service extension is "Future Message
Release".
1) The EHLO keyword associated with this service extension is
"FUTURERELEASE".
2) Two required parameters, the max-future-release-interval and the
max-future-release-date-time, are combined with the EHLO keyword
in the manner specified in [n4].
The max-future-release-interval is a positive integer indicating
the maximum amount of time for which the MSA will hold messages
for future release.
Using ABNF [n2], the syntax of this parameter is as follows:
future-release-integer = %x31-39 *8DIGIT
; integer in the range 1-999999999
; measured in seconds
max-future-release-interval = future-release-integer
The max-future-release-date-time is a timestamp, normalized to
Universal Coordinated Time (UTC), indicating the most remote date
and time in the future until which the MSA will hold messages for
future release.
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Using ABNF [n2], the syntax of this parameter is as follows:
max-future-release-date-time = Internet-style-date-time-UTC
where the format of Internet-style-date-time is defined in [n10].
3) When forming the portion of the EHLO reply containing the
FUTURERELEASE keyword, the keyword is followed by the
max-future-release-interval, and then the
max-future-release-date-time. The keyword and two values are
delimited by spaces.
For example, the ABNF for a continuation line in the EHLO response
that contains the FUTURERELEASE keyword is:
line = "250-FUTURERELEASE" SP max-future-delivery-interval
SP max-future-delivery-date-time
4) One required parameter, the hold-param, is added to the MAIL
command using either the keyword "HOLDFOR" or the keyword
"HOLDUNTIL".
The HOLDFOR parameter value is a future-release-interval,
which is a positive integer indicating the amount of time the
message is to be held by the MSA before release.
The HOLDUNTIL parameter value is a future-release-date-time,
which is a timestamp, normalized to UTC, indicating the future
date and time until which the message is to be held by the MSA
before release.
Using ABNF [n2], the syntax of this parameter is as follows:
future-release-interval = future-release-integer
future-release-date-time = Internet-style-date-time-UTC
hold-for-param = "HOLDFOR=" future-release-interval
hold-until-param = "HOLDUNTIL=" future-release-date-time
hold-param = hold-for-param / hold-until-param
The absence of this parameter on the MAIL command does not imply a
default value for this parameter.
5) The maximum length of a MAIL command is increased by 34 characters
by the possible addition of the hold-param.
6) No additional SMTP verbs are defined by this extension.
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7) This service extension is appropriate only for the SMTP
submission protocol [n3]. This service extension is not
appropriate for standard SMTP [n4].
4.1 Behavior
It is unfortunate to define two seemingly identical ways to indicate
a future delivery time. When the client has both accurate time and
accurate time zone information, either interval or date-time can be
trivally calculated from the other. However, in the current world of
clients, there are clients with accurate local time but no indication
of their time zone, and client without a suitably accurate clock.
Based on the limited facilities available to these time-challenged
clients, it is likely that only one or the other of these mechanisms
will be useful.
It is believed that servers will have accurate time, and can trivally
convert between these mechanisms. It is also accepted that the
protocol and implementation overhead of offering these two mechanisms
is low, and that few interoperability challenges are anticipated.
4.1.1 SMTP client behavior
1) An SMTP client preparing to use Future Message Release MUST first
verify that the MSA supports this extension.
2) An SMTP client using Future Message Release MUST include one, and
only one, hold-param with the MAIL command.
4) An SMTP client using Future Message Release with the "for"
option of the hold-param MUST ensure that the
future-release-interval is less than or equal to the
max-future-release-interval advertised by the MSA.
4) An SMTP client using Future Message Release with the "until"
option of the hold-param MUST ensure that the
future-release-date-time is earlier than or equal to the
max-future-release-date-time advertised by the MSA.
4.1.2 MSA behavior
1) An MSA supporting Future Message Release MUST comply with the SMTP
submission protocol as described in [n3].
2) An MSA supporting Future Message Release MUST NOT advertise this
support (i.e. include the FUTURERELEASE keyword in its EHLO reply)
on any port other than the submission port.
3) An MSA supporting Future Message Release MUST include the
FUTURERELEASE keyword, and associated max-future-release-interval
and max-future-release-date-time parameters, in its reply to the
EHLO command.
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4) An MSA supporting Future Message Release MUST accept a MAIL
command containing a valid hold-param, given that the MAIL command
contains no other errors.
5) An MSA that accepts a message with a request for Future Message
Release indicating the "for" option MUST NOT release the message
until the amount of time specified in the future-release-interval
elapses.
6) An MSA that accepts a message with a request for Future Message
Release indicating the "until" option MUST NOT release the message
until the date and time indicated by the future-release-date-time
occurs.
7) An MSA supporting Future Message Release MUST reject a MAIL
command containing the "for" option specifying a value that is
greater than the advertised max-future-release-interval, or
otherwise invalid.
8) An MSA supporting Future Message Release MUST reject a MAIL
command containing the "until" option specifying a value that
is later than the advertised max-future-release-date-time, or
otherwise invalid.
9) An MSA supporting Future Message Release MUST reject a MAIL
command containing more than one hold-param.
10) An MSA supporting Future Message Release, when rejecting a MAIL
command per 4.1.2.7, 4.1.2.8 or 4.1.2.9, SHOULD supply the reply
code 501 (syntax error in parameters or arguments [n4]) in
the reply.
11) An MSA supporting Future Message Release, when rejecting a MAIL
command per 4.1.2.7, 4.1.2.8 or 4.1.2.9, SHOULD supply the
Enhanced Mail System Status Code 5.5.4 (invalid command
arguments [i1]) in the reply.
4.2 Interaction with the DSN SMTP service extension
The Delivery Status Notification (DSN) service extension is described
in [n7], and DSN message format is described in [n8].
4.2.1 SMTP client interaction with DSN
1) An SMTP client MUST NOT request Future Message Release when
sending a DSN to the MSA.
4.2.2 MSA interaction with DSN
1) If an MSA generates a DSN for a message that includes a Future
Message Release request, the MSA MUST include an Arrival-Date:
field in the machine-readable body part of the DSN.
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2) If an MSA generates a DSN for a message that includes a Future
Message Release request, the MSA MUST include a
Future-Release-Request: field in the machine-readable body
part of the DSN. The value of this field is the value of the HOLD
parameter contained in the MAIL command of the original message.
The Future-Release-Request: field is an extension to the
set of DSN per-message fields described in [n8]. Using ABNF [n2],
the syntax of this new field is as follows:
orig-hold-param-value = ("for;" future-release-interval) /
("until;" future-release-date-time)
; this is the value of the HOLD parm from
; the MAIL command of the original message
future-release-request-field = "Future-Release-Request:"
orig-hold-param-value
4.3 Interaction with the DELIVERBY SMTP service extension
If an MSA supports the Future Message release and Deliver By service
extensions, it is possible for an SMTP client to make simultaneous
requests for future message release and deliver-by times when
submitting a message. A problem will occur if the future message
release time is farther in the future than the deliver-by time. In
order to honor the deliver-by request, the future message release
request has to be ignored. In order to honor the future message
release request, the deliver-by request has to be ignored. This
section addresses that problem. The Deliver By extension is
described in [n6].
4.3.1 SMTP client interaction with DELIVERBY
1) When an SMTP client wishes to use the Future Message Release and
Deliver By extensions with the same message, the client MUST
ensure that the specified deliver-by time is farther in the
future than the specified ("until" option) or implied ("for"
option) future message release time.
4.3.2 MSA interaction with DELIVERBY
1) If an MSA supports Future Message Release and Deliver By
extensions, and receives a message requesting the use of both
extensions, the MSA MUST reject the MAIL command if it determines
that the future message release time is farther in the future than
the deliver-by time.
2) When an MSA is rejecting a MAIL command per 4.3.2.1, it SHOULD
supply the reply code 501 (syntax error in parameters or arguments
[n4]) in the reply.
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3) When an MSA is rejecting a MAIL command per 4.3.2.1, it SHOULD
supply the Enhanced Mail System Status Code 5.5.4 (invalid
command arguments [i1]) in the reply.
4.4 Interaction with the MDN function
The Message Disposition Notification (MDN) function is described in
[n9].
4.4.1 SMTP client interaction with MDN
1) An SMTP client MUST NOT request Future Message Release when
sending an MDN to the MSA.
5. Security Considerations
The Future Message Release service extension presents a number of
security considerations:
1) Unauthorized future-release messages provide a means to
overwhelm the storage of an MSA. An MSA that supports Future
Message Release MUST also support at least one of the
authorization mechanisms enumerated in [n3].
2) Authorized future-message-release without a per-user quota may
also provide a way to overwhelm an MSA's storage. An MSA's
future-release message storage SHOULD be subject to a per-user
quota.
3) If an MSA is imposing a per-user quota on future-release message
storage, and detects that an incoming future-release message will
exceed the user's future-release message storage quota, the MSA
MUST reject the MAIL command.
4) When an MSA is rejecting a MAIL command per 5.3, it SHOULD supply
the reply code 552 (requested mail action aborted: exceeded
storage allocation [n4]) in the reply.
5) When an MSA is rejecting a MAIL command per 5.3, it SHOULD supply
the new Enhanced Mail System Status Code defined for this purpose.
This new status code updates [i1].
X.7.9 Future-release message quota exceeded
There is insuffient per-user quota to queue the message for
future release. This code suggests the client can
submit again only after the per-user queue has drained.
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6) Some element of deception is inherent in the future message
release concept. The message release time is intentionally
delayed past the time it would otherwise be released; hence,
the message delivery time is delayed past the time it would
otherwise be delivered. This extension provides no mechanism for
hiding this from the message recipient. The RFC 2822 message
header, and specifically the Date: field, remain unchanged after
submission. While a sending client MAY elect to place the
future-message-release-time as the date in the Date: field, there
is no requirement or expectation that the Received: fields and
other trace information be modified by the transport system to
further this deception.
6. IANA Considerations
According to the IANA website, this extension will be added to the
list of SMTP extensions on the Mail Parameters webpage once this
draft becomes a Standards Track RFC.
This document defines an additional enhanced status code. At this
time there is no IANA registry for these extension values beyond
publication of this document in the standards-track.
7. Acknowledgments
Much credit for this draft is due to the LEMONADE working group who
through many revisions resulted in fundamental new understandings
of this protocol and corresponding refinement of the implied
requirements and protocol. Special thanks to Mark Crispin for
patiently leading the WG to understand that doing both interval
and date-time was the pragmatically correct approach to the needs
of diverse clients.
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8. Normative References
[n1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[n2] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[n3] Gellens, R. and J. Klensin, "Message Submission", RFC 2476,
December 1998.
[n4] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
2001.
[n5] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[n6] Newman, D., "Deliver By SMTP Service Extension", RFC 2852, June
2000.
[n7] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
Extension for Delivery Status Notifications (DSNs)", RFC 3461,
January 2003.
[n8] Moore, K. and G. Vaudreuil, "An Extensible Message Format for
Delivery Status Notifications", RFC 3464, January 2003.
[n9] Hansen, T. and G. Vaudreuil, "Message Disposition
Notification," RFC 3798, May 2004.
[n10] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps," RFC 3339, July 2002
9. Informative References
[i1] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 3463,
Jauuary 2003.
10. Authors' Addresses
Gregory A. White
6519 Camille Ave.
Dallas, TX 75252
USA
E-Mail: g.a.white@comcast.net
Gregory M. Vaudreuil
Lucent Technologies
9489 Bartgis Ct
Frederick, MD 21702
USA
E-Mail: GregV@ieee.org
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11. Intellectual Property Rights Notice
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12. Copyright Notice and Disclaimer
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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13. Change Log (to be removed upon RFC Publication)
13.1 Changes from -03.txt to -04.txt
1) Changed extension framework to define HOLDFOR and HOLDUNTIL for
the MAIL command (instead of the HOLD parameter).
2) Made wording changes to several of the SMTP client and MSA
behavior requirements
13.2 Changes from -02.txt to -03.txt
1) Rewrote entire draft in terms of future message release instead of
future message delivery. Almost every paragraph of Sections 1
through 5 have been changed.
13.3 Changes from -01.txt to -02.txt
1) Clarified requirements in section 4.1.1, SMTP client behaviour.
2) Removed the requirement that the MSA comply with the SMTP service
extension mechanism, as the list thought this was redundant text.
3) Added requirement that the MSA MUST only advertise this extension
on the submission port.
4) Added requirements stating how to form the reply to a MAIL command
when the future delivery time included with the MAIL command is
greater than the max-allowable-future-delivery-time advertised by
the MSA.
5) Added requirements stating how to form the reply to a MAIL command
when the future-delivery-time and the deliver-by time don't align
properly.
6) Change the level of the requirement of the per-user quota
requirement in Section 5, Security Considerations, from "highly
RECOMMENDED" to "SHOULD".
7) Added requirements stating how to form the reply to a MAIL command
when the MSA detects that the future delivery message will exceed
the user's future delivery quota. This includes the definition of
a new Enhanced Mail System Status Code.
13.4 Changes from -00.txt to -01.txt
1) Removed the Mechanism section, as it pretty much duplicated the
Behavior section.
2) Removed the requirement that an MSA supporting FUTUREDELIVERY MUST
also support the AUTH extension. Removed all of the requirements
referencing the AUTH extension.
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3) Changed requirement for EHLO FUTUREDELIVERY keyword so that a
positive max-future-delivery-interval value MUST be supplied with
that keyword. A value of zero, or no value at all, are no longer
options.
4) Changed the ABNF definition of max-future-delivery-interval and
future-delivery-interval from [1*9DIGIT] to [%x31-39 *8DIGIT].
This change forces these values to be integers in the range
1-999999999.
5) Added section for FUTUREDELIVERY interaction with MDN.
6) Modified the definition of the Future-Delivery-Date: field to
state that the zone in the date-time value MUST be numeric. Since
this field goes in the machine-readable portion of a DSN, this
change was made so the definition matches the definitions of the
other date fields defined in RFC 3464.
7) Rewrote Security Considerations in terms of "authorization"
instead of "authentication."
8) Modified paragraph 1) of Security Considerations to state that an
MSA supporting FUTUREDELIVERY MUST employ at least one of the
authorization mechanisms listed in RFC 2476.
9) Made all (hopefully) of the changes necessary for the draft to be
compliant with ID-NITS and ID-GUIDELINES found on the IETF
website. Made other wordsmithing changes to improve clarity.
13.5 Discussion of -00.txt
As a note, the -00.txt version of this draft was previously published
as draft-vaudreuil-futuredelivery-02.txt. The name of the draft was
changed after the LEMONADE WG voted to make this document a WG item.
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