Blocking mail from bad places

Tue Apr 3 17:45:53 UTC 2007

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On Apr 3, 2007, at 12:19 PM, Thomas Leavitt wrote:

> The current situation with email is flat out insane. There is no  
> other way to describe it.

I'd agree that the situation is bad but certainly not  
uncontrollable.  We've had very good success keeping spam in check  
with a number of technologies while not really having too many  
problem with false positives.  The last 6 months have been  
particularly nice.  About that time we expanded our greylisting  
policy and that alone has made a dramatic difference.  At one point  
before doing any greylisting we were accepting about 500,000 messages  
a day and delivering about 30,000.  Now we accept about 80,000 and  
deliver about 25,000.  That's a much, much more reasonable ratio.

Really I don't think we are being very aggressive with our  
greylisting either.  We currently greylist IP addresses on a handful  
of RBLs and ones that lack valid reverse DNS.  The greylist only  
applies for 5 minutes and then we allow the mail through.  That 5  
minutes though makes all the difference in the world.  We've had 2-3  
senders complain (mostly about invalid reverse DNS) but really I'm  
fine with "fix your shit" for an answer to those people.  If they  
can't then they can just wait the 5 minutes with all the other unwashed.

Will spammers adapt?  Sure.  We've already seen stock spammers who  
are retrying at 5 minutes to the second.  However, this is one of  
those issues where the cost of adapting may just be to high most of  
the time.  Probably easier to just go after the weaker targets.

My other theory on this is that if spammers really do adapt to  
greylisting, then they will have no choice but to actually start  
caring about bounces and clean their mailing lists.  If they don't  
then they just won't be able to keep up with all the queued mail.   
Getting them to clean up their lists in itself would be a more than  
minor victory.

Chris

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Chris Owen         ~ Garden City (620) 275-1900 ~  Lottery (noun):
President          ~ Wichita     (316) 858-3000 ~    A stupidity tax
Hubris Communications Inc      www.hubris.net
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