I am using an edge case of multipart/mixed and find that the
multipart/mix parser in the email package is broken.  See attached
example.  Similar code using cgi.FieldStorage (!) works fine.

The problem happens through the following combination of factors:

1. Content-Length given
2. Content-Transfer-Encoding: 8bit
3. Last two bytes of the part body are '\r\n'

In this case, the final '\n' is removed from the part body, leaving it a
byte short.  Note that interior occurrences of '\r\n' work fine, as does
any other binary data -- it's only a trailing '\r\n' that breaks.

Note that technically perhaps the use of 8bit is invalid; but the same
problem happens when using binary instead.

The problem can be reproduced in Python 3.x using nearly the same demo
by change the cStringIO import to "import io".