Although this is off topic from mailman, I want to add a note on 'greylisting' to prevent spam/worm from reaching mailman list admindb moderation queue. They really are annoying if your list can't be set members only like software support list or webmaster list.
Effect of greylisting: (on my solaris server)
% tail -3000 /var/log/syslog | grep ' 450 ' | wc
561 15708 211654
% tail -3000 /var/log/syslog | grep ' 550 ' | wc
178 4984 54360
% tail -3000 /var/log/syslog | grep ' result:' | wc
17 204 5681
% tail -3000 /var/log/syslog | grep ' result: Y' | wc
7 84 2751
Interpretation: The first test shows the number of smtp mail connections in which the delivery was delayed by greylisting policy (300 seconds). Most of which are spams/worms so that they will not try to connect my server again. The second is for 'user not found'. These are also likely spams/worms but try to send message again and finally rejected. The third test indicate the SpamAssassin test was done, i.e., the recipient was real user. The last test is the number for which the message was marked as spam. Note that 3000 lines of syslog correspond for about an hour on my smtp server.
If I don't use greylisting, more message are tested by SpamAssassin and yield heavier load and further piling up in my admindb queue.
I use Postfix for MTA and Postgrey for greylisting FYI.
Adding REL="nofollow" attributes
Another way to discourage spammers is to add REL="nofollow" to all links in posted messages.
For a simple script and more info, see http://wpkg.org/REL=%22nofollow%22_and_Mailman
Note: adding this attribute to HTML code is controversial.
Last changed on Thu Feb 7 17:38:03 2008 by Tomasz Chmielewski
Converted from the Mailman FAQ Wizard
This is one of many Frequently Asked Questions.