Re: [exim] SORBS

On Fri, Nov 10, 2006 at 11:20:45AM -0000, Hill Ruyter wrote:
> I understand all your points and they are all very valid
> however should it be the case that someone be completely blocked purely on
> the basis of a dynamic IP ?

Obviously any blocking based on information which doesn't
include the contents of the mail in question is not an
appropriate antispam measure because in general you can't
tell whether a mail is spam or not until you've inspected
its contents. Some people claim that presence or absence
of a sending host on a `black list' is additional useful
information for such a classifier, but based on my own
observations I don't believe this. Generally a filter can
determine (at some level of accuracy) whether something is
spam, under a given user's definition, from its contents
and the additional information that the mail passed
through a host which was or was not on a `black list' is
unlikely to change its decision very often. It is easy to
see why this is so: a given user is unlikely to change
their opinion of whether a mail they've received about,
say, opportunities to purchase pharmaceutical products
inexpensively, is desirable based on further information
about the hosts through which it passed.

Nevertheless there are lots of sites which do block mail
based purely on `black lists' of one sort or another, as
you have discovered. Sometimes it is possible to get the
authors of the `black lists' to remove addresses from
them, but generally if you depend on being able to
exchange mail with people at sites run in that fashion all
you can do is try to find another address through which to
relay your mail or some other means to route around the
idiocy. (As you will have seen from email to this list
`black lists' are very popular among a certain sort of
person and these people will strongly resist any argument
against their use.) There is of course no guarantee that
once you find such an address it won't itself be put on a
`black list' and indeed one of the consequences of
blocking on this basis is that the administrator who does
so confers the power to block mail onto the authors of the
`black lists' to exercise arbitrarily.

If you choose to relay, of course, you are then depending
on the competence etc. of the people running the relaying
host, which is more-or-less beyond your control. Wherever
you choose to run a mail server you will need to keep
close watch on as many `black lists' as you can identify
so that you can detect as soon as possible when some idiot
decides to list you and take compensating action (and if
you choose to relay, you trust the operators of the relay
to do so themselves).

--
``The reason that the sun never set on the British Empire
is that God wouldn't trust an Englishman in the dark.'' (Duncan Spaeth)