ISPs blocking SMTP connections from dynamic IP address space

Jez Hancock jez.hancock at
Thu Aug 7 09:52:38 PDT 2003

On Thu, Aug 07, 2003 at 12:34:45PM -0400, Lucas Holt wrote:
> >
> I think we need software that blocks spam out of the box.
> Server Side:
> I've found that most of my time is spent installing addons for sendmail 
> to do virus scanning and spam prevention.  Why don't mail servers have 
> spam assassin, black lists, etc. enabled and installed with a base set 
> of rules to prevent spam?  Every  release of the software would also 
> need to include new rules, but your ip list solution needs updating all 
> the time too.
Exim with exiscan enabled allows you to reject mail considered spam
based on the results of an SA scan.  The hard part is maintaining a
decent blacklist locally if you can't afford the overhead of using
online RBL blacklist servers on a heavily used mail server I would

Another issue with this is what you tell your clients. I recently had a
client who I recommended to a certain ISP who received an email from
that ISP which was nothing short of scare-mongering.

The email was written by the CEO of the ISP, who it appears hadn't a
clue about exactly how the software blocked spam or perhaps wasn't that
good at articulating in layman's terms exactly how spam was to be
blocked.  As a result a number of the ISP's clients were instantly
worried that anything containing swear words or 'make money' or whatever
in the subject would be blocked, which wouldn't be the case (one would

I think a nice alternative is to set a number of different filtering
rules on the MTA so that spam that scores very highly (say over 15 on
the SA scale) is rejected outright, whereas spam that scores relatively
highly on the SA scale has it's subject modified to indicate that the
content is possibly spam.  Again though this could be seen as unwanted
intrusion by some customers...


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