In <20040224210112(_dot_)GM27676(_at_)dumbo(_dot_)pobox(_dot_)com> Meng Weng
Wong <mengwong(_at_)dumbo(_dot_)pobox(_dot_)com> writes:
| But after a quick scan, I can't see that it really discusses the SMTP
| envelope at all; nor what would be an appropriate action to take at a
| forwarding host or end-point host if a header were determined to be invalid.
| Bounce it I guess?
Caller-ID explicitly ignores the SMTP envelope.
Caller-ID's action is to silently sink the message. [...]
I haven't reviewed this published spec for Caller-ID, but I suspect
things haven't changed much.
Without checking the envelope-from, you can't safely bounce email. As
far as I'm concerned, this is A Very Bad Thing. Once you have a known
good evelope-from, you can do lots of other stuff later on and bounce
if you reject the email.
Caller-ID and DomainKeys both need something like SPF or SRS+callbacks
to make them safe to use.
I personally have strong doubts that either Caller-ID nor DomainKeys
can really solve the problem of From: header forging. I also have my
doubts that they won't break a lot of real-world stuff. However, if
they succeed, that is wonderful.
-wayne