On Wed, Sep 10, 2003 at 07:32:29AM -0400, Marc A. Pelletier wrote
The next step is to pre-emptively block email from *ALL* dynamic
addresses. The problem is that there are so many, that the zones
get huge.
I think there is a much stronger reason to avoid trying to block
dynamic addresses: it causes false positives. A well implemented
UA that injects mail via SMTP (with or without the submission
subprotocol) is the "correct" way to do things given that the 'net
was designed for end-to-end communication.
"The 'net was designed for..."
- a clientel consisting of white, male, middle-class military types
and civilians doing reasearch for the military. These people needed
security clearance simply to get on the net, which is why smtp had
no security designed in. This clientel would have no incentive to
spam; doing so would risk their security clearance.
- administration by BOFH admins who knew what they were doing
Today, every fourteen-year-old 133t-hax0r-dude can get on. The vast
majority of residential customers have problems finding the "ANY" key,
and are easy targets for evil people who want to take over their
machines.
I would say that the proper way to handle dynamic addresses is by
behavior control and not by outright blocking.
For whatever reason, some big ISPs can't be bothered. Ask anybody
who's been mailbombed by a stuck virus on a compromised machine, and the
offender's ISP takes forever to shut them down.
Rate limiting comes to mind, as well as error counting.
How does an ISP rate-limit except by routing SMTP transactions through
its own MTAs ? And it's *NOT* really point-to-point communications when
the machine/person at IP address w.x.y.z can be someone totally
different than who connected to you from the same address five minutes
ago. What it all comes down to is that the vast majority of emails sent
direct-to-mx from residential/dynamic IP addresses is spam. If you're
going to accept smtp traffic from another ISP's dynamic IP addresses,
you need some form of authentication. This can be the POP-before-SMTP
hack, or ssh-tunneling, or SSL, or whatever.
--
Walter Dnes <waltdnes(_at_)waltdnes(_dot_)org>
Email users are divided into two classes;
1) Those who have effective spam-blocking
2) Those who wish they did
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