My reading of the RFCs agrees with yours and yes, in response to the
situation I outlined last week with the SGI machine sending bounces to
the Reply-To: address, I have taken just the "extreme" step you suggest.
This is the 2nd time I've had to bounce someone. In both cases my stated
position is that I have only one requirement for people who subscribe to
my lists and that is that their mailbox reside on a system that conforms
to the accepted internet standards. If it does not and puts the list at
risk, you're out. Find your system or get a mailbox on a different one.
(Note that if the person resubscribes with another address, you still
gotta check that he hasn't .forward-ed mail from there back to the
offending system.) In last week's incident the user put up a lengthy
argument, which only ceased when I trotted out the RFCs and pointed him
to specific sections. At that point he found a new mailbox AND went after
SGI customer support to find out how to fix his sendmail.
I too wondered about possible repercussions, but I decided I could safely
stand on the RFCs if someone ever tried to get nasty about it.