[Mimedefang] validating 'possibly forged' helo IP's?

[Kevin A. McGrail]

> > ISPs in my experience don't even really care about setting reverse
> > DNS up.
>
> Isn't it good practice for mail exchanges to have a PTR record?
> I can understand why ISP's don't go to the trouble to rDNS every
> IP in the network, but it would seem to be a good idea to support
> rDNS on their outwardly visible servers.

It's good practice for mail servers because a lot of people block
mailservers without one.  AOL for example.

But the content of the PTR record in my experience can be anything really.
Something like 'look.ma.imaserver.com' would probably work perfectly fine.

However, with only one PTR record available per IP and potentially 10, 100,
1000, more domains handled on that one mail server, how can you use the PTR
data to verify anything?

IMO, it's simply a hurdle and I guess the hopes would be that ISPs serving
residential customers would by default have no reverse ptrs for there IPs so
that mail servers could block based on this.  I'm extrapolating and guessing
here though.

Regards,
KAM