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Re: ISP phishing

  • From: william(at)
  • Date: Wed Jun 29 07:35:25 2005

On Wed, 29 Jun 2005, Mike Leber wrote:

See my other email in regards to this mobile user strawman argument.
Look in the archives for the same arguments against closing open relays.
Current mobile-user arguments against SPF do indeed remind of the anti open-relay battles 5-8 years ago. Not only that but often enough its
the same people who are doing this arguing ... (just look at the main
ietf mail list and you'll see what I mean).

If Alice wants to forward [email protected] to
[email protected] and use SPF or MX+ with [email protected]
presumably she won't block email from her other account and she can check
if she got it right really easy by sending email to
[email protected]
Unfortunately per-user filters for SMTP transmission are notoriously difficult to implement (especially on large scale). Plus you may not
be able to say that email came in forwarded just from SMTP transmission (forwarders often do not leave its own marker, you can try to identify forwarder by EHLO name but that may not be forwarder by some kind of outbound relay server on the forwarding network site).

Another issue is that are doing the forwarding are the ones that
are most often least maintained as far as upgrading software and
enabling new SMTP features. As a result an idea that we will ask
all forwarders to change and identify themselves in forwarded mail
can not happen as quickly as path authentication proponents want.

Now I did propose one solution to this - a way to bypass forwarders
by having origin mail servers add crypto signatures with their own
hostname serving as base and then tie in further path authentication
to cryptographically verified hostname (see paper, I previously
posted, quick link at, and I have more
hope in another system that I'll get to later this year.

William Leibzon
Elan Networks
[email protected]