Use an RESL with SpamAssassin to Greatly Reduce Spam

Emailreg.org provides the Registered Email Send List (RESL) as a free lookup to anyone that would like to use it. It is also provided to those who have registered a domain here at EmailReg.org. The RESL is provided using a system that is similar to a DNS lookup. It is even more similar to a DNSRBL lookup. The RESL, however, requires looking up a DOMAIN and a IP address in order to determine if that IP address is a legitimate sender of email from that DOMAIN.

Append the following to the /etc/mail/spamassassin/local.cf.

header __RCVD_IN_EMAILREG eval:check_rbl('emailreg-trusted', 'resl.emailreg.org.')

header RCVD_IN_EMAILREG_0 eval:check_rbl_sub('emailreg-trusted', '127.0.\d+.0')
describe RCVD_IN_EMAILREG_0 Sender listed at http://www.emailreg.org/
tflags RCVD_IN_EMAILREG_0 nice net

header RCVD_IN_EMAILREG_1 eval:check_rbl_sub('emailreg-trusted', '127.0.\d+.1')
describe RCVD_IN_EMAILREG_1 Sender listed at http://www.emailreg.org/
tflags RCVD_IN_EMAILREG_1 nice net

score RCVD_IN_EMAILREG_0 -100
score RCVD_IN_EMAILREG_1 -100

Restart SpamAssassin

service spamassassin restart

That’s it!

Source(s)
http://www.emailreg.org/index.cgi?p=usage