Steve Kent writes:
Since classic PEM operates in a vanilla RFC 822 environment (though it
could be extended for MIME), and since MOSS requires a MIME environment, it
is not quite accurate to suggest that the two standards overlap.
Unfortunately, this really isn't accurate either. The implication here is that
a "MIME environment" is somehow different than an RFC 822 environment, and this
is not the case.
MIME is designed so that it can be used in multiple different environments. One
of those is old-fashioned Internet mail as specified in RFC821 and RFC822. Any
MIME object can be represented in such a way that it is compatible with such an
environment.
MIME can also be used in ways that are only compatible with SMTP environment
that the 8BITMIME SMTP extension provides.
MIME can also be used in ways that are only compatible with HTTP and the
SMTP environment the BINARY SMTP extension provides.
MOSS does require MIME, and this in turn implies that an environment capable of
supporting MIME be used. But this can be the same vanilla "RFC 822 environment"
that PEM uses. Or you can take advantage of one of the newer environments that
have been defined. (Actually, in the case of signed messages, the inability to
revise the content under the signature leads to all messages being compatible
with unextended RFC821/RFC822.)
Environmental issues are therefore not a significant factor in selecting
between PEM and MOSS.
Ned