[Mimedefang] Blocking spam senders using IPTables?

Aleksandar Milivojevic amilivojevic at pbl.ca
Wed Nov 3 10:31:35 EST 2004

Paul Murphy wrote:
> I'd also be interested in implementing a block based on address range check, so
> perhaps if more than 10 SPAM messages which scored over 10 were received from an
> address block, then the known or estimated range of SPAM senders in that block
> would be blacklisted using IPTables, with a daily review.

Probably not a good idea, since you don't know how big is remote network 
block.  It might be something like /24, but it also might be something 
like /29.  If you blindly assume it is /24, you'll get the spammer 
blocked (maybe, it just might be that one of your users had .forward 
file at remote site, and you can't know that either), but you will also 
penalize everybody else.

Plus, some mailing lists will happily forward spam from time to time, 
one popular example is Linux kernel mailing list...  And there are some 
criminally managed lists such as Bugtraq, that don't forward spam 
(probably because it is moderated), but do some other stuff that might 
trigger things here and there.  So you might just as likely end up 
blocking those, to delight of your users.

Aleksandar Milivojevic <amilivojevic at pbl.ca>    Pollard Banknote Limited
Systems Administrator                           1499 Buffalo Place
Tel: (204) 474-2323 ext 276                     Winnipeg, MB  R3T 1L7

More information about the MIMEDefang mailing list