From: "Theo Schlossnagle" <jesus(_at_)omniti(_dot_)com>
The argument that it breaks forwarders is not a good one. What's the
difference between a forwarder and a spammer? They both lie outside the
control of the domain owner. While a forwarder might be "trusted", that
idea is flawed as well. Spammers will just focus on compromising
machines on the those forwarders networks.
Forwarders can get over it. Procmail can do all sorts of interesting things
to incorporate the original sender's address in a message prefix, and
re-write the forwarded message "From:" line.
*Mailing lists* is a much bigger problem for me, since lots of academic
mailing lists are extremely unlikely to switch to SRS in the academic
lifespan of any of the grad students maintaining the lists. It's why I have
to use "?all" rather than "-all", and why I'm examining the SpamAssassin
code in 3.0 to provide SPF based scoring.