Network Working Group C. Malamud
Internet-Draft June 12, 2003
Expires: December 11, 2003
A "No Soliciting" SMTP Service Extension
draft-malamud-no-soliciting-00.txt
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This note presents an extension to SMTP for an electronic mail
equivalent to the real-world "No Soliciting Sign." By itself, this
extension does little to stop unsolicited bulk electronic mail.
However, the extension gives policy makers in the real world a "hook"
on which to pass anti-spam laws.
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Table of Contents
1. The Spam Pandemic . . . . . . . . . . . . . . . . . . . . . . 3
2. No Soliciting in the Real World . . . . . . . . . . . . . . . 4
3. The No-Soliciting SMTP Service Extension . . . . . . . . . . . 6
3.1 SYSTEM-WIDE-NO-SOLICITING . . . . . . . . . . . . . . . . . . 6
3.2 PER-MESSAGE-NO-SOLICITING . . . . . . . . . . . . . . . . . . 6
3.3 Solicitation Mail Header . . . . . . . . . . . . . . . . . . . 7
4. Hooks for ISPs and Other Policy Makers . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Author's Acknowledgements . . . . . . . . . . . . . . . . . . 12
Informative References . . . . . . . . . . . . . . . . . . . . 13
Normative References . . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . 16
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1. The Spam Pandemic
Spam, otherwise known as Unsolicited Bulk Email (UBE), has become as
one of the most pressing issues on the Internet. One oft-quoted
study estimated that spam will cost businesses $13 billion in
2003.[1] In April 2003, AOL reported that it had blocked 2.37 billion
pieces of spam in a single day. [2] And, in a sure sign that spam has
become of pressing concern, numerous politicians have begun to issue
pronouncements and prescriptions for fighting this epidemic.[3] [4]
A variety of mechanisms from the technical community have been
proposed and/or implemented to fight spam:
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. [5]
o Blacklists are lists of known spammers or ISPs that allow spam.[6]
o Spam filters run client-side or server-side to filter out spam
based on whitelists, blacklists, and textual and header
analysis.[7]
o A large number of documents address the overall technical
considerations for the control of spam [8], operational
considerations for SMTP agents[9], and various extensions to the
protocols to support spam identification and filtering. [10] [11]
[12]
o Various proposals have been advanced for "do not spam" lists, akin
to the Federal Trade Commission's "Do Not Call" list for
telemarketers.[13]
Many of these proposals and services have great merit, however none
of them put an SMTP agent in the process of delivering mail that the
receiver does not wish to receive solicitations. Such a virtual sign
would permit the SMTP delivery service to declare that solicitations
are not desired at this site or by a particular recipient at this
site.
For purposes of this proposal, we'll use the common definition of
spam, which is "Unsolicited Bulk Email." Unsolicited means "not
requested" and bulk means "large in volume." As will be seen in
subsequent sections, we leave the precise definitions of these terms
to policy makers.
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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 Newbury, Massachusetts, for example, requires:
"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." [14]
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 ..." [15]
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.[16]
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."[17] And, in Martin v. City of
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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."[18] Note that the public safety issue applies very much to
email, where viruses and can easily be delivered, in contrast to
telephone 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 spam 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.
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3. The No-Soliciting SMTP Service Extension
Per RFC 2821,[22] two SMTP service extensions are defined:
1. SYSTEM-WIDE-NO-SOLICITING
2. PER-MESSAGE-NO-SOLICITING
3.1 SYSTEM-WIDE-NO-SOLICITING
The SYSTEM-WIDE-NO-SOLICITING extension is a simple Boolean flag,
indicating that no soliciting is in effect 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 flag 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-SYSTEM-WIDE-NO-SOLICITING
No further actions are specified in this extension.
It should be noted that 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 UCB" keyword.[19] 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., [20]).
3.2 PER-MESSAGE-NO-SOLICITING
The PER-MESSAGE-NO-SOLICITING extension specifies that each MAIL FROM
command must identify if this 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
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R: 250-trusted.example.com says hello
R: 250-PER-MESSAGE-NO-SOLICITING
Additionally, the SOLICIT keyword is defined as a parameter for the
MAIL FROM command. It has one value, "yes," which identifies this
message as a solicitation. In turn, the receiving system may decide
on a per-user basis the appropriate disposition of messages:
S: MAIL FROM:<savebigbucks@hotmail.com> SOLICIT=YES
S: RCPT TO:<coupon_clipper@trusted.resource.org>
R: 250 <coupon_clipper@trusted.resource.org>... Recipient ok
S: RCPT TO:<grumpy_old_boy@trusted.resource.org>
R: 550 <grumpy_old_boy@trusted.resource.org>... No spam pls
3.3 Solicitation Mail Header
As specified in RFC 2822,[23] a new header field "Solicitation" is
defined, which has only one value "TRUE":
To: Coupon Clipper <coupon_clipper@trusted.resource.org>
From: Spam King <savebigbucks@hotmail.com>
Solicitation: TRUE
Several proposals, particularly legal ones, have suggested requiring
the use of keywords in the "Subject" header. For example, the State
of California requires that:
"In the case of e-mail that consists of unsolicited advertising
material for the lease, sale, rental, gift offer, or other
disposition of any realty, goods, services, or extension of credit
the subject line of each and every message shall include "ADV:" as
the first four characters. If these messages contain information
that consists of unsolicited advertising material for the lease,
sale, rental, gift offer, or other disposition of any realty,
goods, services, or extension of credit, that may only be viewed,
purchased, rented, leased, or held in possession by an individual
18 years of age and older, the subject line of each and every
message shall include "ADV:ADLT" as the first eight characters."
[21]
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, the semantics of
the header are overloaded. Of course, there is no reason why both
mechanisms can't be used, and in many cases the "Solicitation" header
could be automatically inserted based on the contents of the subject
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line.
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4. Hooks for ISPs and Other Policy Makers
This proposal is not meant to "solve" the spam 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.
By providing a service-level extension to SMTP, this proposal
provides a simple mechanism that allows a system or ISP to put email
senders on notice that mail that is both bulk and unsolicited is not
wanted.
One common criticism of any technical or legal measures to prevent
spam is that the global reach of the Internet makes any such measures
futile. Several points are worth noting:
1. First, anti-spam protests are often pursued through the
Appropriate Use Policy in a service agreement between an Internet
Service Provider and an end-user.
2. Disparity between laws of different jurisdictions is an age-old
problem and many mechanisms have evolved to solve these issues.
In the United States, conflicts of state laws are dealt with
through the courts and a well-established body of law.
3. On an international level, conflicts of law are dealt with
through international agreements, particularly trade agreements.
Thus, if the U.S. believes that spam is a pressing commercial
issue, it will bring the issue into a forum such as the World
Trade Organization, perhaps trading off a stronger agreement on
spam for a more liberal policy on the import of produce.
4. As previously noted, much if not most spam originates from U.S.
citizens. A policy "hook" in the SMTP architecture will thus
prove highly effective if not universally effective.
In summary, no one proposal will solve all issues with unsolicited
bulk email, but adding a mechanism at the SMTP service level provides
one more tool in that fight.
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5. Security Considerations
This proposal does not present additional security complications
beyond those already amply represented in the current architecture
for electronic mail.
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6. IANA Considerations
The proposed service extensions would have to be added to the IANA
"Mail Parameters" registry. The IANA does not maintain a registry of
mail headers, though such a registry would no doubt prove useful.
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7. Author's Acknowledgements
The author would like to thank Rebecca Malamud for many discussions
and ideas that led to this proposal and to Marshall T. Rose for his
input on how it could be properly implemented in SMTP. Dave Crocker
and Paul Vixie provided reviews of the draft and numerous
suggestions. Information about soliciting outside the U.S. was
received from Rob Blokzijl, Jon Crowcroft, Christian Huitema, Geoff
Huston, and Pindar Wong. As always, all errors, omissions,
generalizations, and simplifications are the responsibility of the
author.
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Informative References
[1] Associated Press, "Study: Spam costs businesses $13 billion",
January 2003.
[2] CNET News.Com, "AOL touts spam-fighting prowess", April 2003.
[3] Charles, C., "Schumer, Christian Coalition Team Up to Crack
Down on Email Spam Pornography", June 2003.
[4] Federal Trade Commission, "Federal, State, Local Law Enforcers
Target Deceptive Spam and Internet Scams", November 2002.
[5] Habeas, Inc., "Habeas Compliant Message", April 2003.
[6] Spamhaus.Org, "Register of Known Spam Operations".
[7] Mason, J., "Spamassassin - Mail Filter to Identify Spam Using
Text Analysis", Version 2.55, May 2003.
[8] Crocker, D., "Technical Considerations for Spam Control
Mechanisms", draft-crocker-spam-techconsider-01 (work in
progress), May 2003.
[9] Lindberg, G., "Anti-Spam Recommendations for SMTP MTAs", BCP
30, RFC 2505, February 1999.
[10] Danisch, H., "A DNS RR for simple SMTP sender authentication",
draft-danisch-dns-rr-smtp-02 (work in progress), June 2003.
[11] Daboo, C., "SIEVE Spamtest and Virustest Extensions",
draft-daboo-sieve-spamtest-03 (work in progress), April 2003.
[12] Crouzet, B., "Authenticated Mail Transfer Protocol",
draft-crouzet-amtp-00 (work in progress), June 2003.
[13] Federal Trade Commission, "Telemarketing Sales Rule", Federal
Register Vol. 68, No. 19, January 2003.
[14] The Town of West Newbury, Massachusetts, "Soliciting/Canvassing
By-Law", Chapter 18 Section 10, March 2002.
[15] 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.
[16] U.S. Supreme Court, "Perry Education Association v. Perry Local
Educators' Association", 460 U.S. 37 (1983), February 1983.
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[17] U.S. Supreme Court, "Cantwell v. State of Connecticut", 310
U.S. 296 (1940), May 1940.
[18] U.S. Supreme Court, "Martin v. City of Struthers, Ohio", 319
U.S. 141 (1943), May 1943.
[19] Levine, J. and P. Hoffman, "Anti-UBE and Anti-UCE Keywords in
SMTP Banners", Revision 1.1, March 1999.
[20] Malamud, C., "An Internet Prayer Wheel", Mappa.Mundi Magazine,
August 1999.
[21] State of California, "California Business and Professions
Code", Section 17538.4(g).
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Normative References
[22] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
2001.
[23] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
Author's Address
Carl Malamud
PO Box 300
Sixes, OR 97476
US
EMail: carl@media.org
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