At 9:05 AM -0500 11/28/04, Daniel Feenberg imposed structure on a
stream of electrons, yielding:
It occurs to me that a site that was unwilling to handle policy rejections
during SMTP processing, and hence faced with the choice of returning DSNs
to a possibly forged "From" address or dropping them on the floor, does
have an intermediate choice. They could return the DSN via the connecting
host or the MX for that connecting host. That is, whatever the "From"
address, go back to the connecting host to deposit the DSN into the mail
stream. In many legitimate cases that host will accept mail for that
"From" address, it is very unlikely to accept forged mail unless it is an
open relay.
That is so far from anything resembling rational behavior for any
mail server that I'm hard pressed to respond to it within the decorum
bounds of this mailing list.
I'll just say that I think this is an idea that I pray never sees
application in the real world.
There is already a mechanism "source routing" as the basis for
implementation. RFCs still require the ability to process source routes
for servers, although it is no longer required for clients. In any case,
the connecting host doesn't actually have to do anything special. It just
sees the "mail rcpt" address and either accepts or rejects the message
depending upon its ability to deliver to that user.
I think you might find it useful to read RFC2821 again a bit more carefully.
--
Bill Cole
bill(_at_)scconsult(_dot_)com
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