I think "no 8bit characters in headers" is a reasonable
requirement
No, if we are going to fix this let us do it all the way. We need 8bit in
the headers (at least in the subject line). Unfortunately I don't have the
definite solution to how we should solve the charset problem there :-(
If you want to declare to use non-ASCII part of characters of
ISO 8859-1 with 8th bit set, the definite way of ISO 2022 is to
add a three letter escape sequence "ESC - A" at the beginning of the
string. (For theoretical completeness, you may also add a two letter
sequence "ESC n".) Existing terminals which properly support ISO 8859-1
silently eat the sequences and display what you want.
No charset, no charset problem.
Masataka Ohta