Tony Finch [dot(_at_)dotat(_dot_)at] wrote:
On Wed, 27 Oct 2004, Julian Mehnle wrote:
Crypto will never prevent misdirected bounces, i.e. envelope sender
forgery, though. Only SPF Classic, RMX, and Co. will.
Utter crap. The correct way to fix forgery backscatter is to put a
cryptographic token in the MAIL FROM address on your outgoing email
(e.g. SES or BATV).
Yeah, well, I meant "message crypto". Of course a crypto token in the
envelope sender achieves the goal, but has problems of its own...
This allows you to distinguish between valid bounces and bounces from
forged email. It does not require co-operation with anyone else and
has significantly fewer interoperability problems than SPF.
...such as that it enables replay attacks and thus requires my MTA to keep
track of generated and used up tokens in a database.