I haven't looked at the patch in detail, but if my quick skim is correct, it looks like you are decoding using latin1.  If you don't provide any way to get at the original bytes (which I presume you don't if you have "converted the API to return strings"), then it will be difficult and non-obvious to correctly decode messages using a content transfer encoding of 8bit and some other character set.  (Of course, it is currently impossible to do this using the Py3k email package either, but I'm working on fixing that).