Bob Eager wrote:

Steve Walker wrote:

I wonder how many newsreaders don't cope with them?

They don't have to. The ones that do are obeying the age-old maxim which
says something like be strict in what you generate, and forgiving in what
you accept.

RFC 5536

"The MIME header fields MIME-Version, Content-Type, Content-Transfer-
Encoding, Content-Disposition, and Content-Language are used in
Netnews articles in the same circumstances and with the same meanings
as those specified in [RFC2045], [RFC2183], and [RFC3282]"