The multipart/alternative construct was deemed more useful for
backward compatability to non-MIME readers. This is because the
"alternative" part is in readable ASCII. The use of
multipart/signed infers a requirement that the "signed" text be
transported from sender to recipient intact. In practice, this
would cause a tendency to encode the text for transport
rendering it unreadable by non-MIME readers.
In my experience, exactly the opposite is true. (I suppose this leaves
us agreeing to disagree. :-)
In particular, the Multipart/Signed framework includes an explicit step
during which the data that has been signed is prepared for signature,
i.e., canonicalized. The expected practice is the text will *not* be
encoded for transport, in order to maximize backward compatibility with
non-MOSS aware MIME agents.
In fact, the expected worst case is that text will be encoded with the
quoted-printable algorithm in order to maximize backward compatibility
with non-MIME aware agents (which implicitly provides backward
compatibility with non-MOSS aware MIME agents).
All of this is a "carry forward" of principles adopted by MIME when it
was being designed (and revised).
Jim
binFUKHF8wX3y.bin
Description: application/moss-signature