sendmail, starting in version 8.8.0, simply drops bytes 128-159 from all
incoming header fields.
The underlying problem is that sendmail's code is far from 8-bit-clean.
sendmail's entire rewriting mechanism works with a string format that
assigns special meanings to bytes 129, 130, 133, etc. It can't even deal
with an 8-bit name in the From line.
This could actually turn out to be a Good Thing in that it will
slow down those who want to propagate 8-bit headers until they
are properly defined and their implications are understood.
Actually, it will be a Bad Thing, because it will encourage people to
continue the illegal use of ISO-8859-1, which does not use those
characters and who therefore "get away" with it presently.
Yes, but we may be better off to have less variation in practice.
I'd rather have "just" some combination of encoded-words and raw
8859/1 to deal with, than to prematurely add UTF-8 to the mix.