I can think of a good reason:
TRACKABILITY! I have a DynDns address (as you can see from my return email
address), and I relay a lot of mail through Exim on this box. The reason I
like it is the fact that I can pinpoint exactly where the mail is being
delivered to. As an example of usage, the other day I sent a message to one
of my customers. 2-3 hours later they called up angry saying "where's this
message you were going to send!?". If I was relaying it to my ISP I'd have
to do something like "I sent it 3 hours ago. It made it to MY ISP. Why not
yours, I don't know". Instead I was able to say "Let's see. It sent out
three hours ago, and was accepted by a.mail.server.net." Their response was
"Well, that is our ISP. Can you confirm what time they got it?" I told them
the time in the log, and they said they would check with their ISP. Sure
enough, 30 minutes later they called back, apologizing, stating that their
ISP did not realize that their mail server was not forwarding mail properly.
It was fixed now and shortly after they fixed it, my message arrived to
them.
Example #2:
I sent a message to a customer. They called around two hours later saying
they did not get it. I ran mailq (Symlink to exim) and it reported the
message was still in the Q. So I did a -d 9 force send of the message
(exim -d 9 -M 1234-5678-00) and watched the output. Their ISP's name server
was timing out so we could not obtain the IP for their mx server. Thus Exim
was postponing the message's delivery. I reported this to them and they said
they would call their ISP. Sure enough, on a queue run around 45 minutes
later (when the message's retry time had expired) exim tried again to lookup
the IP, this time was successful, and sent the message.
If I was relaying all my mail through my ISP's mail server (and frankly, I
don't trust my DSL provider's mail server any further than I can throw it!)
I would not have been able to handle either of these situations!
----- Original Message -----
From: "Matthew Palmer" <mjp16@???>
To: <exim-users@???>
Sent: Wednesday, October 30, 2002 2:33 PM
Subject: Re: [Exim] Blacklisting dynamic IP ranges versus dyndns.org
> On Wed, 30 Oct 2002, Alan J. Flavell wrote:
>
> > A topic that's come up a few times lately with us is how to accept
> > mail from 'good guys' who are registered with dyndns.org when their IP
> > is in a range that's otherwise blacklisted as a spam source.
>
> Tell them to relay through their ISP's mail servers. That's what they're
> there for. There aren't a lot of alternatives I'm aware of, unless you
> write a script which takes HELO data (I don't even know if you can get a
> hold of HELO data in Exim), does the forward lookup, and compares that
with
> the originating IP address - but only does so for dyndns.org addresses.
>
> For extra credit, restrict such lookups only to certain dyndns.org
> subscribers - after all, we don't know who's got subdomains there,
possibly
> there are some spammers lurking in the deeper corners.
>
> But using their ISP's mail servers to relay is the correct answer. I
can't
> think of any reason not to do so, short of gross incompetence (in which
> case, a new ISP would be called for).
>
>
> --
> -----------------------------------------------------------------------
> #include <disclaimer.h>
> Matthew Palmer, Geek In Residence
> http://ieee.uow.edu.au/~mjp16
>
>
> --
>
> ## List details at http://www.exim.org/mailman/listinfo/exim-users Exim
details at
http://www.exim.org/ ##
>
>
