[shakna]

I received two emails yesterday with application/octet-stream as part of the inner body, compliant with RFC2046 [0]. Having a Content-Transfer-Encoding of base64 is entirely optional.

It's the default for certain larger email hosts - that's the reason you see it frequently, but that in no way means that it is the _best_ option for a protocol that suggests it's solving the problems of the old one.

[0] https://tools.ietf.org/html/rfc2046#section-4.5.1