Network Working Group C. Malamud
Internet-Draft Memory Palace Press
Expires: July 24, 2004 January 24, 2004
A No Soliciting SMTP Service Extension
draft-malamud-no-soliciting-04
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on July 24, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This Internet-Draft proposes an extension to SMTP for an electronic
mail equivalent to the real-world "No Soliciting" sign. In addition
to the service extension, a new message header and extensions to the
existing "received" message header are described.
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 BCP 14, [RFC2119].
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 The Spam Pandemic . . . . . . . . . . . . . . . . . . . . . 3
1.2 No Soliciting in the Real World . . . . . . . . . . . . . . 3
1.3 A Distributed No Soliciting Extension . . . . . . . . . . . 5
2. The No-Soliciting SMTP Service Extension . . . . . . . . . . 6
2.1 The SYSTEM-WIDE Option . . . . . . . . . . . . . . . . . . . 6
2.2 Solicitation Class Keywords . . . . . . . . . . . . . . . . 7
2.2.1 Note on Choice of Keywords . . . . . . . . . . . . . . . . . 8
2.3 The PER-RECIPIENT Option . . . . . . . . . . . . . . . . . . 8
2.4 Use of Enhanced Mail Status Codes . . . . . . . . . . . . . 9
2.5 Solicitation Mail Header . . . . . . . . . . . . . . . . . . 10
2.6 Insertion of Solicitation Keywords in Trace Fields . . . . . 10
2.7 Relay of Messages . . . . . . . . . . . . . . . . . . . . . 11
2.8 Recommendations for Developers and Administrators . . . . . 11
3. Use of the Extension . . . . . . . . . . . . . . . . . . . . 12
3.1 Relationship to Centralized Approaches . . . . . . . . . . . 14
4. Security Considerations . . . . . . . . . . . . . . . . . . 15
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 15
5.1 The Mail Parameters Registry . . . . . . . . . . . . . . . . 16
5.2 Trace Fields . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3 The Solicitation Class Keywords Registry . . . . . . . . . . 16
5.3.1 Guidance on Keyword Specification . . . . . . . . . . . . . 16
5.4 The Solicitation Mail Header . . . . . . . . . . . . . . . . 17
6. Author's Acknowledgements . . . . . . . . . . . . . . . . . 17
Informative References . . . . . . . . . . . . . . . . . . . 17
Normative References . . . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . 20
A. Status of This Document [To Be Removed Upon Publication] . . 20
A.1 RFC Category . . . . . . . . . . . . . . . . . . . . . . . . 20
A.2 Document Repository . . . . . . . . . . . . . . . . . . . . 21
A.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 21
A.4 Changes From Previous Drafts . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . 23
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1. Introduction
1.1 The Spam Pandemic
Unsolicited Bulk Email (UBE), otherwise known as spam, has become as
one of the most pressing issues on the Internet. One oft-quoted
study estimated that spam would cost businesses $13 billion in
2003.[Ferris] In April 2003, AOL reported that it had blocked 2.37
billion pieces of UBE in a single day. [CNET] And, in a sure sign
that UBE has become of pressing concern, numerous politicians have
begun to issue pronouncements and prescriptions for fighting this
epidemic.[Schumer][FTC]
A variety of mechanisms from the technical community have been
proposed and/or implemented to fight UBE:
o Whitelists are lists of known non-spammers. For example, Habeas,
Inc. maintains a Habeas User List (HUL) of people who have agreed
to not spam. By including a haiku in email headers and enforcing
copyright on that ditty, they enforce their anti-spamming terms of
service. [Habeas]
o Blacklists are lists of known spammers or ISPs that allow
spam.[ROSKO]
o Spam filters run client-side or server-side to filter out spam
based on whitelists, blacklists, and textual and header
analysis.[Assassin]
o A large number of documents address the overall technical
considerations for the control of UBE
[I-D.crocker-spam-techconsider], operational considerations for
SMTP agents[RFC2505], and various extensions to the protocols to
support UBE identification and filtering.
[I-D.danisch-dns-rr-smtp][I-D.daboo-sieve-spamtest][I-D.crouzet-amtp]
o Various proposals have been advanced for "do not spam" lists, akin
to the Federal Trade Commission's "Do Not Call" list for
telemarketers.[FTC.TSR]
1.2 No Soliciting in the Real World
Municipalities frequently require solicitors to register with the
town government. And, in many cases, the municipalities prohibit
soliciting in residences where the occupant has posted a sign. The
town of West Newbury, Massachusetts, for example, requires:
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"It shall be unlawful for any canvasser or solicitor to enter the
premises of a resident or business who has displayed a 'No
Trespassing' or 'No Soliciting' sign or poster. Further, it shall
be unlawful for canvassers or solicitors to ignore a resident or
business person's no solicitation directive or remain on private
property after its owner has indicated that the canvasser or
solicitor is not welcome." [Newbury]
Registration requirements for solicitors, particularly those
soliciting for political or religious reasons, have been the subject
of a long string of court cases. However, the courts have generally
recognized that individuals may post "No Soliciting" signs and the
government may enforce the citizen's desire. In a recent case where
Jehovah's Witnesses challenged a registration requirement in the city
of Stratton, Connecticut, saying they derived their authority from
the Scriptures, not the city. However, the court noted:
"A section of the ordinance that petitioners do not challenge
establishes a procedure by which a resident may prohibit
solicitation even by holders of permits. If the resident files a
'No Solicitation Registration Form' with the mayor, and also posts
a 'No Solicitation' sign on his property, no uninvited canvassers
may enter his property ..." [Watchtower]
Even government, which has a duty to promote free expression, may
restrict the use of soliciting on government property. In one case,
for example, a school district was allowed to give access to its
internal electronic mail system to the union that was representing
teachers, but was not required to do so to a rival union that was
attempting to gain the right to represent the teachers. The court
held that where property is not a traditional public forum "and the
Government has not dedicated its property to First Amendment
activity, such regulation is examined only for
reasonableness."[Perry]
The courts have consistently held that the state has a compelling
public safety reason for regulating solicitation. In Cantwell v.
Connecticut, the Supreme Court held that "a State may protect its
citizens from fraudulent solicitation by requiring a stranger in the
community, before permitting him publicly to solicit funds for any
purpose, to establish his identity and his authority to act for the
cause which he purports to represent."[Cantwell] And, in Martin v.
City of Struthers, the court noted that "burglars frequently pose as
canvassers, either in order that they may have a pretense to discover
whether a house is empty and hence ripe for burglary, or for the
purpose of spying out the premises in order that they may return
later."[Martin] The public safety issue applies very much to email,
where viruses can easily be delivered, in contrast to telephone
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solicitations where public safety is not nearly as much an issue.
This analysis is very U.S.-centric, which may be appropriate given
that the large majority of UBE appears to originate from U.S.
citizens. However, the concept of prohibiting unwanted solicitation
does carry over to other countries:
o In Hong Kong, offices frequently post "no soliciting" signs.
o In the United Kingdom, where door-to-door peddlers are fairly
common, "no soliciting" signs are also common.
o In Australia, where door-to-door does not appear to be a pressing
social problem, there was legislation passed which outlawed the
practice of placing ads under wipers of parked cars.
o In France, which has a long tradition of door-to-door
solicitation, apartment buildings often use trespass laws to
enforce "no solicitation" policies.
o In the Netherlands, where door-to-door solicitation is not a
pressing issue, there is a practice of depositing free
publications in mailboxes. The postal equivalent of "no spam"
signs are quite prevalent and serve notice that the publications
are not desired.
1.3 A Distributed No Soliciting Extension
Many of the anti-spam proposals that have been advanced have great
merit, however none of them give notice to an SMTP agent in the
process of delivering mail that the receiver does not wish to receive
solicitations. Such a virtual sign would serve two purposes:
o It would allow the receiving system to "serve notice" that a
certain class of electronic mail is not desired, whether or not
such a message is properly identified as belonging to that class.
o If a message is properly identified as belonging to a certain
class and that class of messages is not desired, transfer of the
message can be eliminated. Rather than filtering after delivery,
elimination of the message transfer can save network bandwidth,
disk space, and processing power.
This memo details a series of extensions to SMTP that have the
following characteristics:
o A service extension is described that allows a receiving Mail
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Transport Agent (MTA) to signal the sending MTA that no soliciting
is in effect.
o A header field for the sender of the message is defined that
allows the sender to flag a message as conforming to a certain
class.
o Trace fields for intermediate MTAs are extended to allow the
intermediate MTA to signal that a message conforms to a certain
class.
Allowing the sender of a message to tag a message as being, for
example, unsolicited commercial email with adult content, allows
"good" spammers to conform to legal content labelling requirements by
governmental authorities or conventions imposed by "whitelist"
services. For senders of mail who choose not to abide by these
conventions, the intermediate trace fields defined here allow the
destination MTA or a designated intermediate MTA to perform
appropriate dispositions on the received message.
This distributed approach to controlling UBE is advanced as an
alternative to centralized "do-not-spam" lists. The concluding
section of this document details how the decentralized approach would
work in practice and contrasts this approach to a centralized list.
2. The No-Soliciting SMTP Service Extension
Per [RFC2821], a "NO-SOLICITING" SMTP service extension is defined.
The service extension is declared during the initial "EHLO" SMTP
exchange. The extension has one optional parameter and zero or more
solicitation class keywords. Using the notation as described in the
Augmented BNF[RFC2234], the syntax is:
No-Soliciting-Service = "NO-SOLICITING"
( "SYSTEM-WIDE" [ SP Solicitation-keywords ] )
/ "PER-RECIPIENT" )
As will be further described below, the "Solicitation-keywords"
construct is used to indicate which messages are accepted or not. In
the case of the "SYSTEM-WIDE" option, this information is indicated
during the initial "EHLO" exchange. In the case of the
"PER-RECIPIENT" option, this information is not present in the
initial exchange and is instead presented as part of the "MAIL-FROM"
command.
2.1 The SYSTEM-WIDE Option
"NO-SOLICITING SYSTEM-WIDE" indicates that no soliciting is in effect
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for all messages delivered to this system. It is equivalent to the
sign on the door of an office building announcing a company-wide
policy.
The parameter is presented during the initial exchange between sender
and receiver:
R: <wait for connection on TCP port 25>
S: <open connection to server>
R: 220 trusted.example.com SMTP service ready
S: EHLO untrusted.example.com
R: 250-trusted.example.com says hello
R: 250-NO-SOLICITING SYSTEM-WIDE ADV
(The "ADV" keyword is one of several possible values and is described
in the following section.)
A similar proposal was advanced in 1999 by John Levine and Paul
Hoffman. This proposal used the SMTP greeting banner to specify that
unsolicited bulk email is prohibited on a particular system through
the use of the "NO UCE" keyword.[Levine] As the authors note, their
proposal has the potential of overloading the semantics of the
greeting banner, which may also be used for other purposes (see,
e.g., [Malamud]).
2.2 Solicitation Class Keywords
The "NO-SOLICITING" service extension uses solicitation class
keywords to signify classes of solicitations that are not accepted.
Keywords are separated by commas and follow the "SYSTEM-WIDE"
parameter. As described subsequently, solicitation class keywords
are also used with the "PER-RECIPIENT" variant of this extension as
well as with the "Solicitation:" and trace field message headers.
Three solicitation class keywords are defined in this draft:
Keywords Description Reference
--------- -------------------------------- ---------
MAPS-UBE Unsolicited Bulk Email http://mail-abuse.org/
ADV Unsolicited Commercial Email http://www.spamlaws.com/
ADV:ADLT Sexually Explicit Commercial Mail http://www.spamlaws.com/
MAPS-UBE is the standard advanced by the Mail Abuse Prevention System
(MAPS), which states:
An electronic message is "spam" IF: (1) the recipient's personal
identity and context are irrelevant because the message is equally
applicable to many other potential recipients; AND (2) the
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recipient has not verifiably granted deliberate, explicit, and
still-revocable permission for it to be sent; AND (3) the
transmission and reception of the message appears to the recipient
to give a disproportionate benefit to the sender.
Numerous states have adopted the "ADV" and "ADV:ADLT" conventions.
We cite the spamlaws.com site as a reference because it provides an
excellent summary of the definitions and pointers to the relevant
statutes.
There is no default keyword for the service. In other words, the
following example is a "no-op":
R: 250-NO-SOLICITING SYSTEM-WIDE
Additional solicitation class keywords may be defined and registered
as specified in Section 5.3. Multiple solicitation class keywords are
separated by a comma to form a list:
Solicitation-keywords = Solicit-word 0*("," Solicit-word)
Solicit-word = [ "MAPS-UBE" / "ADV" / "ADV:ADLT"
/ x-word / registered-word ]
x-word = ["x-" / "X-"] 1*(wordchars)
registered-word = ALPHA 0*(wordchars)
; registered-word(s) are registered
; with the IANA
wordchars = 1*("-" / "_" / ":" / ALPHA / DIGIT)
Developers should note that a "registered-word" MAY contain a
trailing wild card as part of the specification. See Section 5.3.1
for more details.
2.2.1 Note on Choice of Keywords
This document does not specify which keywords shall or shall not be
used on a particular message. The requirement to use a particular
keyword is a policy decision well outside the scope of this document.
In particular, the three keywords described in this document are for
illustrative purposes only and it is expected that relevant policy
bodies (e.g., a government, ISP, or other institution) will specify
appropriate keywords, the definition of the meaning of those
keywords, and any other policy requirements, such as a requirement to
use or not use this extension in particular circumstances.
2.3 The PER-RECIPIENT Option
The "NO-SOLICITING PER-RECIPIENT" extension specifies that each "MAIL
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FROM" command must identify if a message is a solicitation.
The presence of this extension is identified during the initial
greeting:
R: <wait for connection on TCP port 25>
S: <open connection to server>
R: 220 trusted.example.com SMTP service ready
S: EHLO untrusted.example.com
R: 250-trusted.example.com says hello
R: 250-NO-SOLICITING PER-RECIPIENT
Additionally, "SOLICIT" is defined as a parameter for the "MAIL FROM"
command. The "SOLICIT" parameter is followed by an optional equal
sign and a comma separated list of solicitation class keywords.
The syntax for this parameter is:
Mail-From-Solicit-Parameter = "SOLICIT"
"=" Solicitation-keywords
Note that white space is not permitted in this production.
As an informational message, the "550" or "250" replies to the "RCPT
TO" command may also contain the "SOLICIT" parameter.
The receiving system may decide on a per-user basis the appropriate
disposition of messages:
S: MAIL FROM:<save@burntmail.example.com> SOLICIT=ADV,MAPS-UBE
S: RCPT TO:<coupon_clipper@moonlink.example.com>
R: 250 <coupon_clipper@moonlink.example.com>... Recipient ok
S: RCPT TO:<grumpy_old_boy@moonlink.example.com>
R: 550 <grumpy_old_boy@moonlink.example.com>... SOLICIT=ADV
In the previous example, the receiving MTA returned a "550" status
code, indicating that one message was being rejected. Note that the
implementation also echoes back the currently set keywords for that
user on the "550" error message.
2.4 Use of Enhanced Mail Status Codes
If a session between two MTAs is using both the "NO-SOLICITING"
extension and the Enhanced Mail Status Codes as defined in [RFC3463]
and a message is rejected based on the presence of a "SOLICIT"
parameter, the correct error message to return is "5.7.1", defined as
"the sender is not authorized to send to the destination ...
[because] of per-host or per-recipient filtering."
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2.5 Solicitation Mail Header
Per [RFC2822], a new "Solicitation:" header field is defined which
contains one or more solicitation class keywords.
To: Coupon Clipper <coupon_clipper@moonlink.example.com>
From: Spam King <save@burntmail.example.com>
Solicitation: ADV,ADV:ADLT
Several proposals, particularly legal ones, have suggested requiring
the use of keywords in the "Subject:" header. While embedding
information in the "Subject:" header may provide visual cues to end
users, it does not provide a straightforward set of cues for computer
programs such as mail transfer agents. As with embedding a "no
solicitation" message in a greeting banner, this overloads the
semantics of the "Subject:" header. Of course, there is no reason
why both mechanisms can't be used, and in any case the
"Solicitation:" header could be automatically inserted by the
sender's Mail User Agent (MUA) based on the contents of the subject
line.
2.6 Insertion of Solicitation Keywords in Trace Fields
The "Solicitation:" mail header is only available to the sending
client. RFCs 2821 and 2822 are quite specific that intermediate MTAs
shall not change message headers, with the sole exception of the
"Received:" trace field. Since many current systems use an
intermediate relay to detect unsolicited mail, an addition to the
"Received:" header is described.
[RFC2821] documents the following productions for the "Received:"
header in a mail message:
With = "WITH" FWS Protocol CFWS
Protocol = "ESMTP" / "SMTP" / Attdl-Protocol
Additionally, [RFC2822] defines a comment field as follows:
comment = "(" *([FWS] ccontent) [FWS] ")"
Solicitation Keywords are inserted as comments using the following
production, which is based on the "Mail-From-Solicit-Parameter"
defined in Section 2.3 above:
With-Solicit = "WITH" FWS Protocol
"(" [FWS] Mail-From-Solicit-Parameter [FWS] ")"
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An example of a Received: header from a conforming MTA is as follows:
Received: by foo-mta.example.com with
ESMTP (SOLICIT=ADV,ADV:ADLT) ; Sat, 9 Aug 2003
16:54:42 -0700 (PDT)
It should be noted that keywords presented in trace fields may not
agree with those found in the "Solicitation:" header and trace fields
may exist even if the header is not present. When determing which
keywords are applicable to a particular exchange of messages,
implementors SHOULD examine any keywords found in the "Solicitation:"
header. Implementors MAY examine other keywords found in the trace
fields.
2.7 Relay of Messages
The "NO-SOLICITING SYSTEM-WIDE" service extension, if present,
applies to all messages handled by the receiving Message Transfer
Agent (MTA), including those messages intended to be relayed to
another system.
When relaying a message which was received in which the "SOLICIT"
parameter was set on the "MAIL FROM" command, the MTA MUST also set
the "SOLICIT" parameter when delivering the message to an SMTP server
that supports this extension.
The "SOLICIT" parameter on a "MAIL FROM" command can be derived from
a variety of sources, including receipt of a message from a
conforming SMTP server. An SMTP server MAY, for operational reasons
as defined in Section 7.7 of [RFC2821], set this parameter after
detecting the presence of the "Solicitation:" or extended "Received:"
message header field or by using other system-specific techniques.
Implementers should be aware that the "NO-SOLICITING" service
extension is not a guaranteed end-to-end service. Specifically,
intermediate relays that do not support this service may "lose" the
per-message parameters. However, the "Solicitation:" header and any
trace fields inserted during the message transfer process will
persist, and downstream MTAs MAY use this extension when relaying a
message which was received without this extension.
2.8 Recommendations for Developers and Administrators
Developers that implement the "NO-SOLICITING" service extension
SHOULD NOT enable the service as a default. There are some
indications that some policy makers may view a default filtering in
software as a prior restraint on commercial speech. In other words,
because the person installing the software did not make an explicit
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choice to enable a certain type of filtering, some might argue that
such filtering was not desired.
Likewise, it is recommended that a system administrator installing
software SHOULD NOT enable "PER-RECIPIENT" filtering by default for a
user. Again, individual users should request the service.
The mechanism for an individual user to communicate their desire to
enable certain types of filtering is outside the scope of this
document.
It should be noted that for recipient MTAs, implementation of the
"SYSTEM-WIDE" option is significantly simpler than adding
"PER-RECIPIENT" capabilities. Because "PER-RECIPIENT" is an optional
parameter, it should be noted that:
o A conforming sending MTA MUST provide support for both
"SYSTEM-WIDE" and "PER-RECIPIENT".
o A conforming receiving MTA MAY provide support for either
"SYSTEM-WIDE" or "PER-RECIPIENT" or both.
Implementation of SYSTEM-WIDE on a receiving MTA is fairly trivial.
For example, on the popular sendmail [1] package, a few minor changes
need to be made to three files to provide the appropriate "EHLO"
announcement.
3. Use of the Extension
This proposal is not meant to solve the UBE problem, but offers some
tools that can be used by policy makers, be they governments defining
laws or Internet Service Providers defining appropriate use policies.
The service extension allows a mail recipient to notify the sender
that certain forms of electronic mail are not desired and thus gives
policy makers a mechanism for requiring senders of such electronic
mail to identify their missives any penalties for failure to do so.
To illustrate how the system might work in practice, a simple
hypothetical scenario is presented.
Our scenario posits that the U.S. federal government wants to do
something about spam, but is uncertain about the effectiveness of a
centralized "do not spam" list. Instead, they decide to go for a
more decentralized approach as follows:
1. The first step would be for the government to promulgate a
definition of spam and tie a keyword to that definition. This
definition needs to published in a permanent record of some sort
so that it can be referenced in the following steps. The
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Congressional Record [2] or the Federal Register [3] would both
be considered adequate for this purpose. The definition needs to
include an unambiguous definition of mail covered by the keyword,
a mechanism for a sender to convey that information, and the
legal import of the "NO-SOLICITING" notice and any penalties for
violation thereof. Let us suppose that the keyword to be
registered is ""WMA".
2. The appropriate authority (e.g., the Clerk of the House [4] or an
appropriate executive branch official) would register this
definition with the IANA using the template as described in
Section 5 and sending the completed template to iana@iana.org
[5].
3. To the extent that a proliferation of keywords and conflicting
definitions is considered an issue by policy makers, appropriate
discussions would be held with other countries and the states to
make definitions consistent.
4. Reputable email list maintainers would activate a simple check of
each address on their lists by connecting to the SMTP port of at
least one system indicated by an MX record in the Domain Name
System. If either the "SYSTEM-WIDE" or "PER-RECIPIENT" service
extension matches the "WMA" keyword, the address would be
scrubbed from the list.
5. Reputable users of email lists would add a "Solicitation: WMA"
header to their electronic mail and activate the same simple
check described in the previous step. Any addresses matching the
check would trigger non-delivery of the message and, presumably,
the scrubbing of that address from the list.
6. A system manager, under the guidance of the Administrative
Contact for a domain, would configure "MX" records in the Domain
Name System to designate one or more systems authorized to
receive mail for the domain in question. For each system so
designated, the system manager might enable "NO-SOLICITING
SYSTEM-WIDE WMA". These systems receiving mail on behalf of the
designated domain might also be configured to run a spam
identification utility, such as SpamAssasin [6] or SpamBouncer
[7].
7. End users would configure their mail filters to filter out any
properly tagged messages (e.g., "Solicitation: WMA") and any
messages that are not properly tagged (e.g., in SpamBouncer, the
user might set the "SPAMLEVEL" parameter to "10", which would
filter all messages with a score of 10 or greater using the
software's own algorithms for the detection of probable spam).
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8. Unagressive end users would simply delete their spam folder
periodically. More paranoid end users would check the folder for
false positives and then delete it. A few users might take more
agressive steps. For example, setting the SpamBouncer
"SPAMREPLY" to "COMPLAIN" will automatically dispatch complaints
to ISP abuse lines. If financial penalties for violation of WMA
tagging provisions exist and include a split between the federal
authorities and the filer of a complaint, an additional copy of
the offending mail can be dispatched to a service bureau whose
function is to aggregate large amounts of spam, find the senders,
and then file appropriate procedural motions, receiving a portion
of any recovered monies in return for its efforts.
3.1 Relationship to Centralized Approaches
The overwhelming success of the "do not call" list for telemarketing
have prompted a variety of proposals for similar "do not spam" lists.
Such a list takes a centralized approach to solving the same problem
addressed by this service extension. The centralized approach has
the following potential pitfalls:
o From the point of view of the consumer, a centralized list
operates in batch mode: there is a lag between asserting the
desire to start or stop receiving a certain type of mail and the
implementation of that assertion. In addition, placing an email
address on a centralized list has a significant risk that the list
will be used by some to send even more unwanted mail.
o From the point of view of the government, a centralized list
requires significant resources to administer and maintain.
Because the list contains aggregated information, it is more
valuable to legally irresponsible mailers and thus adequate
security provisions need to be made for the list contents.
o The decentralized approach is cheaper for telemarketers to
implement. From the point of view of the sender of unsolicited
mail, the bulk approach requires a significant data processing
investment to continually "scrub" lists that are received. In
contrast, the decentralized approach requires a simple pattern
match on one address at a time.
It should be noted that the centralized and decentralized approaches
can coexist in some manner. A useful analogy is the field of
copyright. Documents have an inherent copyright and the legal
definition of a copyright violation takes into account the degree to
which the alleged violator knew they were violating the conditions
imposed by the law. One common way to assert coypright is through a
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mark on the document itself, a decentralized approach to copyright
assertion. One can also file a registration with the copyright
office, which adds an additional presumption that adequate notice has
been given.
In the example of spam prevention, there would also be an inherent
right, the right not to received unsolicited commercial mail. The
courts or executive branch, as with copyright, would assess fines
based on a variety of factors, and the degree of notice could
certainly be such a factor. Adding an address to a registry of
do-not-spam addresses, in conjunction with a real-time
"NO-SOLICITING" assertion could both be factors taken into
consideration in levying fines or taking other corrective actions.
4. Security Considerations
This extension does not provide authentication of senders or other
measures intended to promote security measures during the message
exchange process.
In particular, this document does not address the circumstances under
which a sender of electronic mail should or should not use this
extension and does not address the issues of whether consent to send
mail has been granted.
This might lead to a scenario in which a sender of electronic mail
begins to use this extension well before the majority of end users
have begun to use it. In this scenario, the sender might wish to use
the absence of the extension on the receiving MTA as an implication
of consent to receive mail. Non-use of the "NO-SOLICITING" extension
by a receiving MTA SHALL NOT indicate consent.
5. IANA Considerations
There are four IANA considerations presented in this draft:
1. Addition of the "NO-SOLICITING" service extension to the Mail
Parameters registry.
2. Documentation of the use of comments in trace fields.
3. Creation of a Solicitation Class Keywords registry.
4. Creation of a "Solicitation:" mail header, which does not
currently raise any IANA considerations.
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5.1 The Mail Parameters Registry
The IANA Mail Parameters registry documents SMTP service extensions.
The "NO-SOLICITATION" service extension would need to be added to
this registry as follows.
Keywords Description Reference
------------ ------------------------------ ---------
NO-SOLICITING Notification of no soliciting. [<this draft>]
The parameters subregistry would need to be modified as follows:
Service Ext EHLO Keyword Parameters Reference
----------- ------------ ----------- ---------
No Soliciting NO-SOLICITING SYSTEM-WIDE [<this draft>]
No Soliciting NO-SOLICITING PER-RECIPIENT [<this draft>]
5.2 Trace Fields
The Mail Parameters registry would need to be modified to note the
use of the comment facility in trace fields to indicate Solicitation
Class Keywords.
5.3 The Solicitation Class Keywords Registry
A new registry (or a subregistry of Mail Parameters) would need to be
established for Solicitation Class Keywords. The registry would
contain the following fields:
1. Keyword name (e.g., "MAPS-UBE").
2. Keyword description (e.g., "Unsolicited Bulk Email").
3. Keyword reference (e.g., "<this draft>").
Per the policies outlined in [RFC2434], it is recommended that the
IESG request the IANA to appoint a Designated Expert to administer
this registry. Authority for solicitation class keywords in this
registry will come in some cases from published RFCs, but in other
cases will come from applicable laws or regulations. It is
recommended that any non-RFC derived solicitation class keywords be
documented in future informational RFCs to provide a consistent set
of references.
5.3.1 Guidance on Keyword Specification
A set of keywords beginning with a common prefix may be registered
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with the IANA by specifying the prefix followed by wild card
specified as a single asterisk ("*") and shall be considered a single
registry entry. The "keyword reference" field of the registry SHOULD
contain a reference that documents the values this solicitation class
keyword may contain if the trailing wild card is specified in the
"keyword name" field of the registry.
Note to Developers: In designing client and server solutions based
on this extension, it is important to remember to design your code
to take into account the possible use of these trailing wildcards.
See the "Solicitation-keywords" production in Section 2.2 for
valid characters and delimiters.
This facility can be used to insert a "score" or category tag by an
intermediate MTA. For example, a solicitation class keyword "WMA:*"
might be used as follows:
Received: by foo-mta.example.com with
ESMTP (WMA:SBRule:Haven_Domain,WMA:SBScore:10) ; Sat, 9 Aug 2003
16:54:42 -0700 (PDT)
5.4 The Solicitation Mail Header
There is currently no registry defined for mail headers. If such a
registry were to exist, the "Solicitation:" header field would need
to be added to it.
6. Author's Acknowledgements
The author would like to thank Rebecca Malamud for many discussions
and ideas that led to this proposal and to John C. Klensin and
Marshall T. Rose for their extensive input on how it could be
properly implemented in SMTP. Eric Allman, Steven M. Bellovin, Kent
Crispin, Dave Crocker, Curtis Generous, Paul Hoffman, John Levine,
Keith Moore, Ned Freed, Paul Vixie, and Pindar Wong kindly provided
reviews of the draft and/or suggestions for improvement. Information
about soliciting outside the U.S. was received from Rob Blokzijl, Jon
Crowcroft, Christian Huitema, Geoff Huston, and Pindar Wong. John
Levine pointed out the contrast between this proposal and "do not
spam" lists. As always, all errors and omissions are the
responsibility of the author.
Informative References
[Assassin]
Mason, J., "Spamassassin - Mail Filter to Identify Spam
Using Text Analysis", Version 2.55, May 2003, <http://
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www.mirror.ac.uk/sites/spamassassin.taint.org/
spamassassin.org/doc/spamassassin.html>.
[CNET] CNET News.Com, "AOL touts spam-fighting prowess", April
2003, <http://news.com.com/2100-1025-998944.html>.
[Cantwell]
U.S. Supreme Court, "Cantwell v. State of Connecticut",
310 U.S. 296 (1940), May 1940, <http://
caselaw.lp.findlaw.com/scripts/
getcase.pl?court=US&vol=310&invol=296>.
[FTC] Federal Trade Commission, "Federal, State, Local Law
Enforcers Target Deceptive Spam and Internet Scams",
November 2002, <http://www.ftc.gov/opa/2002/11/
nenetforcema.htm>.
[FTC.TSR] Federal Trade Commission, "Telemarketing Sales Rule",
Federal Register Vol. 68, No. 19, January 2003, <http://
www.ftc.gov/os/2002/12/tsrfinalrule.pdf>.
[Ferris] Associated Press, "Study: Spam costs businesses $13
billion", January 2003, <http://www.cnn.com/2003/TECH/
biztech/01/03/spam.costs.ap/index.html>.
[Habeas] Habeas, Inc., "Habeas Compliant Message", April 2003,
<http://www.habeas.com/services/hcm.htm>.
[I-D.crocker-spam-techconsider]
Crocker, D., "Technical Considerations for Spam Control
Mechanisms", draft-crocker-spam-techconsider-02 (work in
progress), May 2003.
[I-D.crouzet-amtp]
Crouzet, B., "Authenticated Mail Transfer Protocol",
draft-crouzet-amtp-01 (work in progress), October 2003.
[I-D.daboo-sieve-spamtest]
Daboo, C., "SIEVE Spamtest and Virustest Extensions",
draft-daboo-sieve-spamtest-04 (work in progress), October
2003.
[I-D.danisch-dns-rr-smtp]
Danisch, H., "A DNS RR for simple SMTP sender
authentication", draft-danisch-dns-rr-smtp-03 (work in
progress), October 2003.
[Levine] Levine, J. and P. Hoffman, "Anti-UBE and Anti-UCE Keywords
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in SMTP Banners", Revision 1.1, March 1999, <http://
www.cauce.org/proposal/smtp-banner-rfc.shtml>.
[Malamud] Malamud, C., "An Internet Prayer Wheel", Mappa.Mundi
Magazine, August 1999, <http://mappa.mundi.net/
cartography/Wheel/>.
[Martin] U.S. Supreme Court, "Martin v. City of Struthers, Ohio",
319 U.S. 141 (1943), May 1943, <http://
caselaw.lp.findlaw.com/scripts/
getcase.pl?court=US&vol=319&invol=141>.
[Newbury] The Town of West Newbury, Massachusetts, "Soliciting/
Canvassing By-Law", Chapter 18 Section 10, March 2002,
<http://www.town.west-newbury.ma.us/Public_Documents/
WestNewburyMA_Bylaws/chapter18>.
[Perry] U.S. Supreme Court, "Perry Education Association v. Perry
Local Educators' Association", 460 U.S. 37 (1983),
February 1983, <http://caselaw.lp.findlaw.com/scripts/
getcase.pl?court=US&vol=460&invol=37>.
[RFC2505] Lindberg, G., "Anti-Spam Recommendations for SMTP MTAs",
BCP 30, RFC 2505, February 1999.
[ROSKO] Spamhaus.Org, "Register of Known Spam Operations",
November 2003, <http://www.spamhaus.org/rokso/
index.lasso>.
[Schumer] Charles, C., "Schumer, Christian Coalition Team Up to
Crack Down on Email Spam Pornography", June 2003, <http://
www.senate.gov/~schumer/SchumerWebsite/pressroom/
press_releases/PR01782.html>.
[Watchtower]
U.S. Supreme Court, "Watchtower Bible & Tract Society of
New York, Inc., et al. v. Village of Stratton et al.", 122
S.Ct. 2080 (2002), June 2002, <http://
caselaw.lp.findlaw.com/scripts/
getcase.pl?court=US&vol=000&invol=00-1737>.
Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
Malamud Expires July 24, 2004 [Page 19]
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[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC
3463, January 2003.
URIs
[1] <http://www.sendmail.org/>
[2] <http://thomas.loc.gov/>
[3] <http://www.gpoaccess.gov/fr/>
[4] <http://clerk.house.gov/index.php>
[5] <mailto:iana@iana.org>
[6] <http://spamassassin.org/index.html>
[7] <http://www.spambouncer.org/>
[8] <mailto:carl@media.org>
[9] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-03.html>
[10] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-04.html>
[11] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-02.html>
[12] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-03.html>
[13] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-01.html>
[14] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-02.html>
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[15] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-00.html>
[16] <http://trusted.resource.org/no-solicit/
draft-malamud-no-soliciting-01.html>
Author's Address
Carl Malamud
Memory Palace Press
PO Box 300
Sixes, OR 97476
US
EMail: carl@media.org
Appendix A. Status of This Document [To Be Removed Upon Publication]
A.1 RFC Category
This document will be submitted for publication as a Proposed
Standard.
A.2 Document Repository
The source for this document can be found at http://
trusted.resource.org/no-solicit.
A.3 Discussion
Discussions of this draft may be directed towards the ietf-smtp
mailing list which can be found at http://www.imc.org/ietf-smtp/.
Comments may be sent directly to the author at carl@media.org [8].
A.4 Changes From Previous Drafts
Changes from draft-malamud-no-soliciting-03 [9] to
draft-malamud-no-soliciting-04 [10]:
o The Note on Open Issues has been removed and the abstract has been
made more precise.
o All examples now use subdomains of example.com.
o The "No-Soliciting-Service" production has been changed to make
clear that a set of keywords is not presented when the
"PER-RECIPIENT" option is used. See Section 2.
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o A Note on Keywords has been added to make clear that the initial
three keywords choosen were simply to bootstrap the registry and
that the matter of which keywords to use and the definition of
those words is a policy decision well outside the scope of this
document. See Section 2.2.1.
o Solicitation Class Keywords are now carried as a comment to the
"ESMTP" protocol and additional language has been added clarifying
the relationship of keywords in "received:" headers to those in
the "Solicitation:" header. See Section 2.6.
o Some language has been added to further clarify what should happen
when dealing with a server that doesn't support the extension. See
Section 2.7.
o The Security Considerations section has been made more explicit.
See Section 4.
o The Solicitation Class Keywords Registry has been clarified to
permit the use of a trailing wildcard in the "keyword name" field.
See Section 5.3.
Changes from draft-malamud-no-soliciting-02 [11] to
draft-malamud-no-soliciting-03 [12]:
o A discussion of Open Issues has been preprended to the document
and comments are requested.
Changes from draft-malamud-no-soliciting-01 [13] to
draft-malamud-no-soliciting-02 [14]:
o A real-world example of how the proposed service extension could
be used has been added (see Section 3).
o A discussion of the relative implementation difficulty of
"SYSTEM-WIDE" versus "PER-RECIPIENT" has been added (see Section
2.8).
o A discussion of the relationship of this proposal to centralized
"do not spam" lists has been added (see Section 3.1).
Changes from draft-malamud-no-soliciting-00 [15] to
draft-malamud-no-soliciting-01 [16]:
o The two service extensions previously proposed (
"SYSTEM-WIDE-NO-SOLICITING" and "PER-MESSAGE-NO-SOLICITING") have
been collapsed into a single "NO-SOLICITING" service extension (
See Section 2).
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o "PER-MESSAGE" has been changed to "PER-RECIPIENT" to more properly
express the operation of the extension (see Section 2.3).
o A solicitation class keyword syntax is introduced to allow
different kinds of unsolicited mail to be considered (see Section
2.2).
o The "Solicitation:" header has been supplemented with an extended
"Received:" header syntax (see Section 2.6).
o A discussion of the use of Enhanced Mail Status Codes has been
included (see Section 2.4).
o A more extensive IANA Considerations section has been added,
including creation of a Solicitation Keywords registry (see
Section 5).
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Malamud Expires July 24, 2004 [Page 25]
