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[ietf-smtp] quoted-unprintable ?

2021-03-21 12:41:26
Over on another list we have been musing about CHUNKING and BINARYMIME.

CHUNKING is easy to implement (I added it to my MTA in about an hour) but 
BINARYMIME
is extremely painful on systems where the native line ending is not \r\n 
because you
have to parse MIME bodies to figure out when to change line endings and when 
not to.

The advantage of BINARYMIME over base64 is that base64 is 33% bigger since it 
encodes
six bits per octet rather than 8.  It occurs to me that since everone these days
supports 8BITMIME, one could invent a quoted-unprintable encoding that encodes 
only
the characters that are special, CR LF NUL.  (To play it safe I'd also encode 
0xff).
This gets you about a 2% size increase and stays compatible with 8BITMIME.

This seems totally obvious.  Has anyone proposed it before?

I realize that there is a severe chicken and egg problem here since you 
wouldn't use it
unless you knew your recipient could handle it.  I suppose one could add an 
EHLO keyword,
but MTAs don't downgrade on the fly any more, particularly since that means 
they would have
to redo DKIM and ARC signatures.

R's,
John

PS: I also realize that the sensible way to send a message with a giant 
attachment is
to put the attachment on a web server and use message/external-body, but that 
doesn't seem
all that well supported, either.

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