We wouldn't mind switching to a world of using BDAT/BINARYMIME (we support
both, but don't advertise BINARYMIME), but when coupled with DKIM, it
becomes harder, since if we switch to generating cte:binary messages and
signing them, or accepting such messages, how do we forward them to hosts
that don't handle them?
I get the impression that for most people, the 25% bloat for base64 isn't
a big enough deal to be worth a lot of effort to upgrade all the required
software to handle binary attachments. If you really care that much, you
might as well put the attachments on a web server somewhere and use
message/external body with a pointer to where it's stored. That's been in
the MIME standard for 20 years.
It's kind of the same problem with SMTPUTF8, of course.
Yes, although with SMTPUTF8 we made a fairly clear distinction that you're
on the bus or you're off, and an entire mail site either supports it or
not. The experimental version had a bunch of fallback options that failed
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