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March 2003 - Spam Email Filtering Changes
The following changes have been made to the
Spam/Virus Email Filtering being
done on the CS mail servers.
- Spamhaus RBL Blocking - Effective March 18th, 2003,
we have enabled the blocking of
spam from senders listed by
spamhaus.org.
This change is in sync with UITS starting to do the same
blocking on the IU central mail servers. The block list
maintained by spamhaus.org is not particularly aggressive, which
means that the chances of blocking non-spam email is low.
However, the list is effective at blocking the most
egregious spammers so it should result in a significant
reduction in spam.
- Vipul's Razor - Effective March 18th, 2003, we
have enabled the Vipul's Razor checks in our
PerlMX configuration.
Vipul's Razor
(aka. SpamNet) is a distributed and constantly updating catalog of
spam in propagation. This catalog is used by our PerlMX
filters to classify spam and should result in more effective
identification of spam.
- PerlMX Probability Change - The PerlMX filtering works by assigning
a probability to each email that it is spam (from 0-100%). When
the probability reaches a set threshold, the Subject: line of the
message is rewritten to include '[SPAM: ]'.
Effective March 5th, 2003, this threshold is being changed from
50% to 60% in an attempt the reduce the number of non-spam messages
that have the '[SPAM: ]' tag added to the
Subject: line. This will also result in more spam passing through
without the '[SPAM: ]' tag, so there are
clearly tradeoffs. However, the absolute value of this spam
probablility is still readily available in the X-Perlmx-Spam: header
which is still being added to all messages with no changes.
Please see the Spam
Filtering FAQ Entry for all the details of how to automatically
filter spam. You are urged to use the X-Perlmx-Spam: header to
do this filtering rather than the '[SPAM: ]' tag
in the Subject: line so that future refinements in the PerlMX
spam probability threshold
do not affect your mail filtering. If you are currently
using the '[SPAM: ]' tag to do filtering, you
may have to make some adjustments to your filter rules to compensate
for the new change in the threshold.
The virus scanning that is performed has not been modified.
Any comments or questions on this subject should be submitted
using the CSG Help Desk.
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