On Mon, 26 Mar 2007, Robert Story wrote:
> On Fri, 23 Mar 2007 18:39:59 -0400 (EDT) Dean wrote:
> DA> Real anti-spam groups at large ISPs don't use reverse DNS for spam
> DA> filtering. There have been attempts to do so in the past, but those
> DA> ended in (sometimes well-publicized) disasters.
>
> This is patently and provably false. AOL clearly states that "AOL's mail
> servers will reject connections from any IP address that does not have
> reverse DNS (a PTR record)."
They may claim this, but it isn't true.
> SpamHaus is a rather well know spam-fighting organization, and they
> clearly state that having reverse DNS is 'highly desirable.' [2]
They have been associated with other lame ideas.
> DA> Assuming an 'apparent inability to update reverse tree' is a false
> DA> assumption:
>
> But you can't dictate other peoples assumptions. Assumptions are often
> based on ones personal experiences, and it's perfectly reasonable for
> different people to make different assumptions.
Sorry. Wrong. Its not 'perfectly reasonable' to make false assumptions.
> DA> The fact that the reverse tree doesn't match something the
> DA> remote site thinks should be there, doesn't mean that the IP address
> DA> user is unable to update the reverse.
>
> Nobody is saying that that is the case.
Ted said that.
> What the spam-fighters are saying is "based on my own experiences,
> more often than not a system (without reverse DNS|with a reverse DNS
> record matching a certain pattern) is not a valid source of mail." In
> some cases, they may be wrong. But its their decision to make.
Its their decision to make in a free society. They are free to be
unreasonable (some constraints--can't violate laws, etc). However, it is
quite another thing to describe unreasonable assumptions as being
scientificially honest and reasonable.
> DA> Further, the definition of what is useful to the IP user doesn't have to
> DA> be "useful" to the remote site for spam-filtering.
>
> Indeed. Neither side can force the other side to do what they want. But
> a mail admin is completely within their rights to say "if you can't
> bother to provide reverse DNS, I won't accept your mail."
They may be within their rights. They may not be within their rights.
Laws control the situation when the admin works for an ISP. Laws also
control the situation where the admin participates in a unlawful group
boycott.
But assuming are within their rights to be unreasonable, then they can
be unreasonable. They just can't tell others that they are
'scientifically reasonable'.
> This is no different that a restaurant with a "No shirt, no shoes, no
> service" policy.
Sorry. Wrong. Laws apply to ISPs serving the public who have a contract
with their customers. However, public health policy requires "no shirt,
no shoes, no service". That policy has a scientific basis.
The arbitrary, capricious, and unreasonable 'no reverse dns' policy has
no scientific basis.
> DA> So reverse DNS entries provide no information on which a spam-score can
> DA> be based. This is why using reverse DNS for spam-scoring has been a
> DA> disaster everytime it has been tried. [the proponents who say it works
> DA> don't use it on a large scale, and don't care if a great deal non-spam,
> DA> legitimate email is lost]
>
> I again refer you to [1], which is certainly a large scale mail system.
Except that they don't practice that policy.
And there is still no reasonable scientific basis for such a policy.
--Dean
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