GPU email antispam measures

We have taken a variety of steps to reduce the amount of junk electronic mail that we and our users receive. Please do not adopt these for yourself (especially with our local list of bad places) without making sure you agree with all the policy decisions we've made. They include:

IP rejection

Using a SunOS 4.1.4 kernel modification written by Paul Kern, we reject IP packets from a number of networks primarily used by spammers, as well as some persistently open relay sites that don't otherwise send us any good mail and the like. For the use of people on campus, here is our rejection list (as of Sept 29 1997). Similar effects can be obtained by using loopback routes (a route to the network you want not to talk to that points to 127.0.0.1) if you don't want or can't use this patch.

TCP Wrappers rejection

Part of our antispam modifications to our mailer (Zmailer 2.2e10) is the use of Wietse Venema's TCP Wrappers. Note that we have made some custom modifications to our TCP Wrappers source, to allow regular expression host names and CIDR netmask lengths; our hosts.deny file (as of Sept 29 1997) will not be too useful to you straight without them. Please read our hosts_access.c patch file to see what new compilation option you need to enable things.

Rejection of bad SMTP HELO greetings

Using a standard feature of Zmailer 2.2e10, our mailer, we reject various sorts of bad SMTP HELO greetings. This is also a convenient and relatively lightweight place to reject some people we don't want to talk to due to spam. Here is a somewhat edited version of our smtpserver.conf file, as of Sept 29 1997. Please do not adopt it without making sure you agree with all the decisions.

Zmailer antispam modifications

We've made a number of modifications to Zmailer 2.2e10 to both block spammers relaying through us and allow us to reject various sorts of email spam and email spammers.

If you don't use the software we do

A number of our measures are specific to our software, particularly to Zmailer 2.2e10, our mailer (although they should be adoptable to most any Zmailer 2.2 version). Zmailer 2.99, an evolved version of our mailer, apparently has its own anti-spam measures in its current version; other current Unix mailers such as qmail and exim do as well, while sendmail 8.8.5 can be configured to have such. Our IP blocking can be adopted to use loopback routes, or any IP firewall support that your kernel has. The general resources at abuse.net may be helpful, especially spam.abuse.net.

Further information

Our email antispam software is part of our antispam software that we are making available to the Internet community.