The End-To-End Internet (was Re: Blocking MX query)

Joe St Sauver joe at
Wed Sep 5 21:15:07 UTC 2012

Izaac <izaac at> commented:

#I suspect your ISP is also stripping <sarcasm> tags.  Let's try it out
#   You can tell that tcp port 25 filtering is a highly effective spam
#   mitigation technique because spam levels have declined in direct
#   proportion to their level of deployment.  Today, we barely see any
#   spam on the internet due to amazing ability of these filters to
#   prevent bad people from sending bulk email.
#Was that properly marked?

Actually, not sure sarcasm tags are appropriate.

1) Port 25 blocks target direct-to-MX spam delivered by bots.

2) The Spamhaus CBL tracks the level of bot spam currently seen,
including breaking out statistics by a number of factors.

3) Currently, the US, where port 25 filtering is routinely deployed by
most large ISPs, is ranked 158th among countries when you consider botted
users on a per capita basis:

4) While that's not perfect (after all, there are still at least 133,811 
listings for the US), on a PER-CAPITA basis, it's not bad -- that's just 
~0.055% of US Internet users that are infected, relative to some countries 
where the rate of detected infection (based on spam emission) may be 4 to
5% or more.

So yes, actually, port 25 blocks *DO* tend to be effective in reducing 
bot-delivered email spam.

Does this mean that port 25 blocks are the ONLY measure that is required
to control spam? No, absolutely not. But it does clearly help.



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