I thought I had understood from the discussion in Santa Fe that an
(unescaped) end-of-line in quoted printable was always to be interpreted
as 0D hex, 0A hex, regardless of the local convention for representing
ends-of-lines in text files. I don't see this spelled out quite so
clearly in the current MIME draft.
However, it wouldn't hurt to restrict the types of conversion that can
be done by a relaying MTA. Such conversions should always be to a
"safer" format. So, ordering the content-transfer-encodings as follows:
BINARY
8BIT QUOTED-PRINTABLE BASE64
7BIT
you can only convert to something further to the right.
Keith