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Re: a header authentication scheme
I guess I wasn't clear. Sorry. Let me try again.
1. Quoting the time isn't good. If I'm allowed 150 tries and can bounce
some mail off your server to read the bounce messages, I can guess when
you'll process a message.
2. Quoting the "with" ID may provide protection, depending on whether
the ID is guessable.
3. A receiver can make its IDs less guessable. A few bytes of randomness
are easily obtained. (A receiver cannot easily make the time of day
more difficult to predict.)
4. Most MTA authors seem eager to implement anything that helps against spam.
Conclusion. Quoting the "with" ID is good, and the MTAs that currently
have guessable IDs will change that quickly if spammers ever exploit
(In a different message, someone mentioned that there's no reason to
allow such processing before the last hop. There is, IMO: It's too
difficult to do otherwise. For example, suppose teamx@xxxxxxxxxxx is an
alias for local user Alice and remote user bob@xxxxxxxxxxxx For mail to
teamx@xxxxxxxxxxx, the example.com MTA is last hop for one user, not
for the other.)