Tony Finch wrote:
BATV is just a variant of SRS: it requires MTAs to rewrite
the envelope sender.
No, BATV envelope rewriting occurs at the MSA and nowhere
else.
You could also do it at all mailouts, in Keith's terminology
"somewhere" (once) in the MON (Mail Originating Network).
And of course it only works if you undo it later at the MX,
reject any forged bounces, accept good bounces decodig BATV.
It is much less problematic than SRS.
That's not at all clear. The "bounces to" fraction can't use
it easily. They want to use "their" MAIL FROM whereever they
submit mail.
Then identifying backscatter isn't trivial, empty Return-Path
and Auto-Submitted are clear, what else ? I have a rather
impressive list of rules to catch this crap, because it was
not allowed to report it as spam with SpamCop in 2004.
Last but not least it only protects the forged address at the
MX of this address, it has no effect for receivers accepting
and later maybe bouncing this crap.
With an SPF FAIL the complete "accept and later maybe bounce"
part can be avoided. Dito delivery / forward, an SPF FAIL
blocks the crap a.s.a.p. at the first MX.
BATV can only block (some) bounces hitting the forged sender.
Nevertheless it's as you said unrelated to SRS. With BATV MXs
+ corresponding mailouts have to change what they do today if
they want to protect their users - minus notorious "bounces to"
fans. The "bounces to" fans are a PITA in any STD 10 scheme.
While SRS affects only some "551-alias-forwarders", and only if
they want to stay in business using this particular trick: SRS
is not the only game in town.
Bye, Frank