The End-To-End Internet (was Re: Blocking MX query)
Joe St Sauver
joe at oregon.uoregon.edu
Wed Sep 5 16:15:07 CDT 2012
Izaac <izaac at setec.org> 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: http://cbl.abuseat.org/countrypercapita.html
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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