[Mimedefang] Blocking spam senders using IPTables?

Paul Murphy pmurphy at ionixpharma.com
Tue Nov 2 09:49:22 EST 2004


> Watch out for mail services that forward e-mail to your 
> users.  Think this:
> A user has an MSN account that gets a lot of spam, and 
> that user sets his MSN account to forward to his local 
> mailbox.  Blam!  You no longer receive _any_ email from MSN.

Accepted - that's why I'd only want to use this approach to target persistent
and readily identifiable spammers.  By blocking using this technique, you'd be
accepting that any matching system would effectively cease to exist as far as
you are concerned.

The problem I'm trying to address is where your system is flooded by messages
from addresses which belong to spammers, and despite greylisting and MD/SA
scoring it as 20+ and sending a 500/571 permanent error, they keep trying at the
same rate.  At the moment, it is an annoying background trickle, but I can see a
tidal wave in the distance because for every site which does sensible blocking,
there are 100 more who will accept the message, and so it is never worthwhile
for them to edit their lists to remove the addresses which fail.  Some would
argue that returning a permanent error for spam is incorrect, but that's my
policy, it works for me, and it has the support of the directors here.  If I can
cut my bandwidth usage by 5% and reduce the load on my MD/SA system by
eradicating the garbage from this one company, the effort will be worth it.

Best Wishes,

Paul Murphy
Head of Informatics
Ionix Pharmaceuticals Ltd
418 Science Park, Cambridge, CB4 0PA

Tel. 01223 433741
Fax. 01223 433788

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