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Re: Which Spam Block List to use for a network?

On Wed, Jun 23, 2004 at 09:01:24PM +1000, Russell Coker wrote:
> On Wed, 23 Jun 2004 18:23, Blu <blu@daga.cl> wrote:
> > Well yes. Maybe I oversimplified. What I do is a callback to the MX of
> > the envelope sender to see if it accepts mail to him/her. If not, the
> > mail is rejected with an explicative 550.
> You aren't the only one who does that.  I have found one other person who does 
> that and who happens to have their mail server in an address range that's 
> black-listed.  So when I sent mail to them their mail server made a call-back 
> to mine, my server rejected that and their mail server then generated a 55x 
> code that tried to summarise the code from mine.  Then my mail server took 
> that and made it into a bounce message.

Of course I am not the first one doing this. In fact Exim4 has buitin
capability to do so.

> The resulting message was something that I could not decipher even though I 
> have 10 years of experience running Internet mail servers!  All I could do 
> was post a message to a mailing list I knew the person was subscribed to and 
> inform them that their server was borked in some unknown way.

:) Well, my approach is not that fancy. I just check if the callback
passes the RCPT, and if not, issue a 550 with a short message telling
that my host will not accept mail that cannot be answered. I don't
expect end users to read a bounce, but many of them forwards the bounce
to customer service instead and in some cases it has been enough to
whitelist a server.

> What would the average Internet user do in such a situation?
> The typical 55x message about a DNSBL rejection is clear enough that most 
> people can get some idea of what to do (IE phone the person, use a different 
> mail server, etc).

In my experience, end users in general are not able to interpret a
bounce message and they complain to admins in the best case. In the
worst case, they do nothing.

> The call-back idea may be good if you have a domain totally full of clueless 
> morons who only receive mail from skilled administrators who have experience 
> in dealing with call-back systems.  But if you have average people exchanging 
> email with other average people (the common case) then it will make things 
> worse not better.

I am not willing to deal with all the sites which reject mail from my
servers for the most diverse reasons and every one with a different
way of dealing with the problem, if any. If a foreign server is
rejecting mail from me, without me having done anything harmful, then
the problem is theirs and not mine. It is the administrator of that
server who has to explain to his users why he is rejecting legitimate


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