[Mimedefang] filter_relay

[Ben Kamen]

Let me iterate that better as I knew after reading what I wrote that I
would get a response like you describe...

I'm not saying an ISP (let's use ComCast as an example) would need to list
DNS and NOT list rDNS or vice-versa....

In sendmail, DNS can match, not match (forged) or not exist (no Record).

ComCast could definitely use DHCP to update the DNS servers and
selectively so. So the A record could be static while the reverse could be
dynamic set on a different but still make-sense scheme for trouble
shooting.

To sendmail though, they wouldn't *match* and that would be the key. They
would still resolve forward and reverse with make-sense query answers, but
the A wouldn't match the PTR and that's what would be key to sendmail.

Maybe I haven't thought it all the way through, but that would be a nifty
thing to do for the spam problem.


  -Ben

p.s. I sure do wish that big ISP's would have available the list of
subdomains. I like to block subdomains of bigger domains (like
il.comcast.net or client.comcast.net) telling the users to use the ISP's
mail server. (I still access from comcast.net, just not the subdomains
there of.)



On Mon, 1 Nov 2004, Aleksandar Milivojevic wrote:

> Ben wrote:
> > Where that would help up is if the ISP's purposefully set up DNS for
> > DHCP and dialup addresses to NOT be correct... and instantly, all those
> > typically zombied addresses would become useless....
>
> Actually, the trend is opposite.  More and more ISP's are dynamically
> updating DNS so that each user has distinct DNS name (for example, cable
> users more and more often have MAC address of their Ethernet card as DNS
> name).  Something like dynamic DNS.  This speeds up resolving of abuse
> complaints.  Give them the DNS name, and they know who it is, they don't
> need to look into (usually huge) logs to find out who was using
> particular IP address at particular point in time.  It also gives
> advanced customers a reason to use this ISP instead of the other.
>
> Anyhow, even if ISP's start to set up DNS incorrectly for DHCP and
> dialup customers, viruses and worms would simply adapt to it.  No gain
> there.  And we end up with screwed DNS, resulting in slower response of
> ISP's to abuse complaints.