Ned,
I think that putting any kind of header stripping (especially
on SMTP output) into your MTA is exceedingly poor judgement on your part;
it's that kind of nonsense that gave us LISTSERV and the violence that
it does to Internet messages, by default (!!). The worst part is that
unlike you, the author of LISTSERV doesn't regret his poor judgement at
all - nay, he revels in it, despite the problems that it causes all
over the world.
In my view, you must NEVER acceed to the demand to do header
stripping in the MTA - that will keep up the pressure on the UA vendors
to fix their broken code. If the MTA vendors perform header stripping
then the UA vendors are wrongly let off the hook. If this sounds like
an uncompromising view, that's because I have been badly, badly burned
by exactly this sort of thing, and I find it reprehensible that UA
vendors don't do their jobs, AND that MTA vendors would even consider
trying to make up for those bums.
I think that the best thing that you could do in that situation
is become a UA vendor - with a fixed UA for those environments whose
UA's are broken. As the saying goes, this is an opportunity, not a
problem.
Erik E. Fair apple!fair fair(_at_)apple(_dot_)com
Postmaster
Apple Computer, Inc.