There's a problem hiding in the claims that deflate-8bit and friends can
be sent over 8BITMIME-supporting channels. Consider a MIA sending a
message with deflate-8bit body to a SMTP server announcing 8BITMIME.
If the server isn't prepared to reject unknown charsets in the body of
messages (and which server is?), it will accept the message and thus
the responsibility for delivery.
The next hop doesn't support 8BITMIME. No problem. This is an
intelligent server that acts by the gateway model of rfc1652 and tries
to recode the offending body parts. Whooops... bounce. :-(
Am I missing something?
This is nothing new; nothing requires that servers in possession of an 8bitMIME
message currently be capable of downgrading. Per RFC 1652 section 3, they
already have the option of returning a bounce if the next hop doesn't support
8bitMIME.
It is entirely possible that this encoding will fail to deploy if 8bitMIME
support isn't sufficiently widespread. But it is even more likely that this
will fail to catch on if clients don't add the necessary support.
But we won't know until we try.
Ned