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FAQ: Current Usenet spam thresholds and guidelines

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Tim Skirvin

May 3, 2009, 3:03:47 AM5/3/09
Archive-name: usenet/spam-faq
Posting-Frequency: weekly
Last-modified: 1998/11/10
Maintainer: (Tim Skirvin)
Original-Author: (Chris Lewis)

Current Spam thresholds and guidelines.

This article is intended to describe the current consensus spam thresholds
and ensure that the definitions of these terms are available and consistent.
It is believed that most, if not all, spam cancellers use these terms and
definitions in their work; however, many other people use the terms
inappropriately, which leads to confusion in discussions. This is an
informal FAQ aimed at clarity and understanding, not anal-retentive

Excessive Multi-Posting (EMP) has the same meaning as the term "spam"
usually carries, but it is more accurate and self-explanatory. EMP means,
essentially, "too many separate copies of a substantively identical

"Substantively identical" means that the material in each article is
sufficiently similar to construe the same message. The signature is
included in the determination. These are examples of substantively
identical articles:

- byte-for-byte identical messages
- otherwise identical postings minimally customized for
each group it appears in.
- advertising the same service.
- articles that consist solely of the same signature
- articles which consist of inclusions of other user's
postings, but are otherwise identical.

Cross-posting means that a single message appears in more than one group.
Most newsreaders allow you to specify more than one group in a posting.

Excessive Crossposting (ECP) refers to where a "lot" of postings to more
than one group each have been made.

Some people think cross-posting is "bad". In and of itself, it's good
behaviour - it allows you to reach more groups with less impact on the net.
Especially if you set the Followup-to: header to one group. It is "bad"
when it's done to attack newsgroups or provoke flamewars (like cross-posting
how to cook a cat between alt.tasteless and, but this is beyond
the scope of this FAQ.

This author considers the term "spam" to mean excessive postings of
EMP and/or ECP variety. That is, "spam", is a generic term for several
different things. The term was originally supposed to mean EMPs only, but
most people use "spam" to mean "any excessive posting".

A spam, EMP, or ECP therefore refers to a posting that has been posted to
many places. There is a consensus that there is a point at which it is
abuse, and is subject to advisory cancellation.

A formula has been invented by Seth Breidbart which attempts to
quantify the degree of "badness" of a spam (whether EMP or ECP) as a
single number. The Breidbart Index (BI) is defined as the sum of the
square roots of n (n is the number of newsgroups each copy was posted

Example: If two copies of a posting are made, one to 9 groups, and one
to 16, the BI index is sqrt(9)+sqrt(16) = 3+4 = 7.

The BI2 (Breidbart Index, version 2) is an experimental metric, which
may eventually replace the BI. It is calculated by computing the sum
of the square roots of n, plus the sum of n, and dividing by two. Eg:
one posting to 9, and one to 16 is

(sqrt(9) + sqrt(16) + 9 + 16) / 2
( 3 + 4 + 9 + 16 ) / 2 = 32 / 2 = 16

The BI2 is more "aggressive" than the BI, intended to cut off the "higher
end". BI allows about 125 newsgroups maximum. BI2 allows a maximum of 35.

A slightly less aggressive index is the SBI (Skirvin-Breidbart Index); it
is calculated much the same as the BI2, but sums the number of groups in
the Followup-to: header (if available), rather than the newsgroups. Eg:
one posting to 9 groups, and one to 16 with followups set to 4 is

(sqrt(9) + sqrt(16) + 9 + 4) / 2
( 3 + 4 + 9 + 4 ) / 2 = 20 / 2 = 10

Except in nl.*, where the SBI is followed, the BI2 and SBI are not used to
determine whether a spam is cancellable.

The thresholds for spam cancels are based _only_ on one or more of the
following measures:

1) The BI is 20 or greater over a 45 day period.
2) is a continuation of a previous EMP/ECP, within a 45 day
sliding window. That is: if the articles posted within the
past 45 days exceeds a BI threshold of 20, it gets removed,
unless the originator has made a clear and obvious effort to
cease spamming (which includes an undertaking to do so
posted in This includes "make
money fast" schemes which passed the EMP/ECP thresholds
several years ago. This author recommends one posting
cross-posted to no more than 10 groups, no more often than
once every two weeks (a BI of 3).

A single posting cannot be cancellable - to reach a BI of 20, it would
have to be cross-posted to 400 groups. This isn't possible due to
limitations in Usenet software.

These thresholds nominally apply to all hierarchies - not just the Big-8
and alt.*. Many hierarchies have more restrictive rules, which are decided
upon and enforced by their users and administrators; they may also opt out
of the cancellations, at the discretion of the same users and admins.

These cancels have nothing whatsoever to do with the contents of the
message. It doesn't matter if it's an advertisement, it doesn't matter if
it's abusive, it doesn't matter whether it's on-topic in the groups it was
posted in, it doesn't matter whether the posting is for a "good cause" or
not - spam is cancelled regardless, based on _how many times_ it was said
and not _what_ was said.

Administrators wishing to ignore spam cancels can "alias out" the site
"cyberspam", and the cancels will not affect your system. This is normally
done at your feed site, but patches are available for INN to allow you to
reject spam cancels on your own system. Ask in
if you need this patch.

Further literature on posting etiquette and related information:

The newsgroup news.announce.newusers

"What is Usenet", by Salzenberg, Spafford and Moraes

"What is Usenet? A second opinion.", by Vielmetti

"FAQ: Advertising on Usenet: How To Do It, How Not To Do It", by Furr

"A Primer on How to Work With the Usenet Community", by Von Rospach, et al

"Rules for posting to Usenet", by Horton, Spafford & Moraes.

"Emily Postnews Answers Your Questions on Netiquette", by Templeton et al

Numerous books and publications on Usenet, such as O'Reilly's "Stopping
Spam" (Schwartz and Garfinkel), the "Whole Internet Guide and Catalog"
(Krol), "Usenet Handbook" (Harrison), etc.

"Cancel Messages: Frequently Asked Questions", by Skirvin

RFC 1855 - Netiquette Guidelines

The above FAQs are also mirrored at various sites, including as,,,,,, etc.

A mailing list has been set up to assist those wishing to post commercial
advertisements on Usenet in a responsible fashion. Email your questions to

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