Subject: Re: [Asrg] New proposal for spam blocking: Greylisting

From: Yakov Shafranovich <[email-masked]>
Date: Fri, 20 Jun 2003 14:01:57 -0400

At 09:32 AM 6/20/2003 -0700, Dave Crocker wrote:

>YS> Lets say a spammers has gained control over a specific IP address for an X
>YS> amount of time. He normally sends out 1M messages via that IP. So now to
>YS> get around this block, he will send out 2M messages retrying delivery. 
>This
>YS> increases his costs slightly but not to the point where it becomes
>YS> unprofitable.
>
>right.
>
>
>YS> The reason why spammers have not tried this approach yet
>YS> become this blocking method has not been widespread.
>
>right.

Lets say to fight this spammer trick email hosts will now reject messages 
after 2 times, then the spammers adjusting and sending 3M messages, now 
reject value stands at 3 times, spammers send 4M messages, ad infinitum. 
This would increase costs of sending email since it would have to be stored 
longed and retried longer. HOWEVER, at a certain point (number of rejects), 
spamming will become too costly although I think that reject point is very 
large. Also, there is a reject point at which the sending MTAs will think 
that the message is really undeliverable. The question is where two of 
these points intersect. This sounds like something Eric Brunner was 
discussing at one point.

This is basically an economic approach - you are increasing the cost of 
each sent message by forcing the sender to store it longer and use more 
network resources sending it. The same goal would be accomplished by adding 
email postage but this approach works without changing the existing 
infrastructure. What you are basically doing is imposing cost on ALL users 
of the system by forcing them to use network resources multiple times.

Yakov  

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From: Dave Crocker <[email-masked]>
Date: Fri, 20 Jun 2003 11:29:55 -0700

Yakov,

YS> Lets say to fight this spammer trick email hosts will now reject messages
YS> after 2 times, then the spammers adjusting and sending 3M messages, now
YS> reject value stands at 3 times, spammers send 4M messages, ad infinitum.
YS> This would increase costs of sending email since it would have to be stored
YS> longed and retried longer. HOWEVER, at a certain point (number of rejects),
YS> spamming will become too costly although I think that reject point is very
YS> large.

as well as the cost to those sending legitimate mail, as well as the
cost to the receiving sites to process these rejected postings.

so, large-scale use of this facility will do an excellent job of
providing a deprivation of service attack.  unfortunately, the attack
will be experienced by everyone, not just the bad guys.

YS> This is basically an economic approach - you are increasing the cost of
YS> each sent message by forcing the sender

blunt instrument.

d/
--
 Dave Crocker <mailto:[email-masked]>
 Brandenburg InternetWorking <http://www.brandenburg.com>
 Sunnyvale, CA  USA <tel:+1.408.246.8253>, <fax:+1.866.358.5301>

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From: Evan Harris <[email-masked]>
Date: Fri, 20 Jun 2003 13:50:04 -0500 (CDT)

> of the system by forcing them to use network resources multiple times.

Exactly, except that the system as described only incurs the penalty the
first time a relationship is established.  And that affects spammers much
more than legit senders.

Evan