Description:

Email::MIME is nice and handy. With header_str and body_str (since 1.900),
you don't need to encode everything by yourself. Just pass flagged
(decoded) utf-8 strings, and you'll get what you want. However, it only
works when you send utf-8 encoded emails. In Japan, there're still some
email clients that only understand iso-2022-jp (jis) encoded emails, and
its popularity persuaded the Encode maintainer (who's also Japanese) to
include its support (since version 2.11, with
Encode::MIME::Header::ISO_2022_JP written by Makamaka). I want it to be
supported by Email::MIME, but it's too specific and nonsense for the rest
of the world. That's why I write this mixin instead of asking to add extra
bit to Email::MIME.