D J Bernstein <djb(_at_)cr(_dot_)yp(_dot_)to> writes:
The Pine people say that they use X-Sender/X-X-Sender because some
unidentified mailing-list programs look at Sender/X-Sender. If this is
true, what were the authors of those programs thinking?
It is true. LISTSERV will use the Sender header in preference to the From
header as the address to perform actions on, to the degree that if you try
to subscribe to a LISTSERV mailing list and your mail has a Sender header,
it will add the contents of that header to the list, not your From header.
I don't know what they were thinking, but from discussions that I've had
with Eric Thomas, it was apparently entirely intentional and not due to
any sort of confusion over what the headers are for, and it's a decision
that he defended with some degree of heat.
I've not used a LISTSERV list again with a Sender header; after that
extremely frustrating and unfruitful exchange with him, I turned off
generation of the Sender header in Gnus (which is similarly using it as a
mostly broken security feature). I don't know if, despite that exchange,
it was later fixed.
--
Russ Allbery (rra(_at_)stanford(_dot_)edu)
<http://www.eyrie.org/~eagle/>