My [Phil Karn] position on Comcastidiocy

[David Farber <dfarber () cs cmu edu>]

Begin forwarded message:

From: Phil Karn <karn () ka9q net>
Date: January 19, 2008 8:04:51 PM EST
To: dave () farber net
Cc: ip <ip () v2 listbox com>
Subject: Re: [IP] My position on Comcastidiocy

A few comments on port 25 blocking:

Everybody seems to assume that blocking direct usage of port 25  
somehow stops spam.

BUT HOW??!?

Exactly HOW does forcing outbound mail to take an unnecessary hop  
through the
ISP's outbound MTA stop spam? Does the MTA have some sort of magic spam
recognizer? If so, why can't it be used by every inbound MTA?

The closest thing we have to a magic spam recognizer is Spam Assassin.  
It (or an
equivalent package) is ALREADY in use by nearly every inbound MTA. How  
does
duplicating this function in an outbound MTA -- or even *having*  
mandatory
outbound MTAs -- help the spam problem?

Forcing outbound mail through a common MTA actually makes it MORE  
difficult for
the receiving MTAs to handle spam. Were the mail to come directly from  
the
sender's IP addresses, blacklists of offending addresses can be  
maintained. But
when all mail from each ISP is forced through a single MTA, it all  
comes from a
single IP address that cannot be blacklisted. Sometimes the  
originator's IP
address can be discerned from the mail headers, but there is no  
universal
standard for this and in any event it's harder to do.

Let's assume a magic spam recognizer exists. Assume further that we  
consider it
mandatory at the originating ISP. But its implementation in a  
mandatory outbound
MTA STILL does not follow!! The magic spam recognizer could passively  
monitor
end-to-end connections to port 25. They would proceed unhindered  
unless spamming
is detected. The ISP would then notify the user and take further  
action at its
discretion, e.g., interrupting service if it's clear he's part of a  
botnet.

Passive stream monitoring clearly requires far less resources than a  
mandatory
MTA. MTAs are infamous resource hogs. Users often complain of long  
delays in
their outbound mail, as can be expected when everyone is forced to use  
them for
no good reason. Indeed, users should be active ENCOURAGED to minimize  
their use
of ISP resources by delivering their mail directly to its destinations  
when
possible.






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