Re: The 'failure' of SMTP RE: DNS Choices: Was: [ietf-dkim] Re: Last Call: 'DomainKeys

On Wed, 22 Nov 2006, Michael.Dillon@btradianz.com wrote:
>
> Mail servers will still exchange messages with known and trusted peers.
> A new mail server operator will have to arrange a trusted peer
> relationship with one or more existing operators at some point in the
> hierarchy. A mail user will have a trusted relationship with a local
> server operator. Many messages will have to be relayed because there is
> no one-level trust relationship between sender and recipient. Mail will
> flow along the chain of trust. And everybody will be motivated to keep
> those chains intact because when they break, messages stop flowing.

This sounds like the Usenet architecture, or the BGP architecture.

Usenet did not escape spam. Spammy usenet servers were not reliably cut
off - certainly the trust relationships between server operators did not
provide an effective way to stop spam. Your last sentence above is the
reason why: keeping legitimate communication working is more important
than the inconvenience of spam.

You can apply the same logic at the level of BGP routing: there
are trust relationships between networks, some of which are clean and some
of which are infested with criminals. The latter spoil it for the rest of
us but they are still not cut off.

For a third example of reluctance to punish the innocent, look at the
hatred directed at DNS blacklists that deliberately block people who are
unlucky enough to be too close in network space to spammers.

Given this, your proposed architecture is just as vulnerable to botnets as
the open SMTP architecture. There are always going to be enough admins who
don't cut off infected machines and who also have enough legitimate
customers that their upstreams won't cut the whole network off. This will
be enough to poison the well.

Tony.
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