Well, it's two years later, but I did look at this during the sprints at PyCon, though I didn't get as far as posting it then (I only just now rediscovered the patch on my laptop).

Python3 no longer has a "binary" flag on base64mime.encode, so here is a proposed patch for Python3.  I'm not sure if this should be backported or not, but I'm leaning that way.  Theoretically it should be only an improvement, but I can easily imagine unix-only programs unknowingly depending on the previous non-translation of newlines.  Still, since email is about intermachine communication and this clearly makes it more RFC compliant, the change is a legitimate bug fix and the chance of breakage is relatively small.

Tests are still needed.