--On Tuesday, February 28, 2012 11:31 +1100 Mark Andrews
Well with paper mail you can have mail from multiple people.
Someone has to physically post it, but it can have multiple
signatures. There should be no reason for email to not support
it. Note SMTP doesn't need to support it.
Indeed. And, yes, the SMTP backward-pointing address in the
MAIL command is really a sender address, not a from address.
I agree with Ned -- deprecating features that poor
implementations handle poorly would leave us without email. It
is far more worthwhile to spend energy telling people to fix
their garbage implementations than to start deprecating features
that are very useful on occasion, even if lots of folks don't
use them and aren't aware they are there. The use of "+" in
subaddresses is at least an equally good example: lots of folks
don't know it is possible; a number of MUAs, a larger number of
web interfaces of various flavors, and a few MTAs treat it is
invalid; but, still...
p.s. it has been a while, but I've occasionally used
multiple-address "From:" on IETF mailing lists when I wanted to
make it completely clear that a message was produced jointly,
e.g., from WG co-chairs.