ISP port blocking practice

Randy Bush randy at
Tue Sep 7 14:00:56 UTC 2010

>> i keep hearing that, but am having a hard time finding supporting data.
> Might see the stats from - by AS.  Then compare
> the stats on a non port 25 filtered network (they have stats by AS) to
> stats on a network that is filtered on port 25
> The networks that are filtered on port 25 will of course have any bots
> on that network originating spam by other means (social networks,
> webmail scripting etc), or other types of nastiness (DDoS etc).  But
> you won't find them mailing out direct on port 25.
> The bots are very much there - and if the port 25 filtering were to be
> taken out, you'd at once see the increase in spam volumes.

thank you.  this make sense.  i'm more focused on the receiving end and
signatures.  so more of the same spam does not bother me much.  but i
can see that pure count would matter to many.


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