Daniel Kahn Gillmor writes:
I'd bet the number of users of non-MIME-aware text-only MUAs receiving mail from mailman that are incapable of wading through a bit of extra MIME boundary info on otherwise text/plain messages is vanishingly small.
Not vanishing. I'll add my testimony to Mark's that we see complaints related to added MIME parts (mostly from people who read the text/html alternative when it is kept, I think, but there are some people still using broken old MUAs, and the real hurt is when somebody's boss's MUA doesn't display the legal BS at the bottom -- neither the boss nor his lawyers are interested in "but we can't do anything about broken MUAs").
Most of those folks are probably at least used to seeing it as a result of the overwhelming predominance of multipart/alternative on today's SMTP network.
For some reason, no, that doesn't seem to be the case.