I'll try to make this my last word on the subject, since the appropriate forum
for this discussion is probably the new verification sub-group, and I haven't
jumped through the necessary hoops to gain posting privs there.
Jon Kyme wrote:
But then, I still can't see what's wrong with tweaking the MAIL FROM.
In an off-list message, Jon clarified that he was alluding to the following
document.
http://spf.pobox.com/draft-mengwong-sender-rewrite-01.txt
I make the following observations.
* Sender rewriting is vulnerable to abuse as a mail relay unless the
implementing MTA generates unique return addresses. (See "Hash Secrets" in
the referenced document.) VIA has no such vulnerability.
* If "Hash Secrets" are used, then sender rewriting may lose its value as a
diagnostic trace of the forwarding path. VIA is always useful as a diagnostic
trace.
* If "Hash Secrets" are used, the implementing MTA must maintain several days
of secret-to-email-addresse mapping data, or use a reversible cryptographic
encoding. VIA requires no cryptographic techniques or additional maintenance
of state.
* Sender rewriting can run afoul of address length limitations unless a "Hash
Secret" regime is chosen to avoid it. VIA faces no such problem, as it does
not overload any existing field.
* Sender rewriting makes the return path trustable, so that there is no
concern of returning a bounce message to an unrelated third party. VIA can
provide no direct assurance about the return path, but if you accept the
lemma that "forwarded mail is only accepted from explicitly trusted parties",
then VIA effectively provides the same assurance, as trusted parties provide
trustworthy data.
* Sender rewriting introduces network overhead into the bounce process, as
bounces will be "un-forwarded" through the MTAs they were initially forwarded
through. VIA maintains the traditional "direct" method of returning bounces.
* I consider "anonymous remailers" to be "remailers" rather than "forwarders".
If an anonymous remailer wishes to allow replies and/or bounces, it will be
obliged to use a cryptographically secure mapping between its own addresses
and the addresses of its clients. VIA is not relevant to this case.
Regards,
TFBW
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