UnicodeEncodeError

[kbiernat]

While parsing attached email I get an exception:
UnicodeEncodeError: 'utf-8' codec can't encode character '\udcea' in position 5595: surrogates not allowed

This only occurs in Python 3.5, in Py27 it's fine.
django-mailbox==4.6

https://github.com/watchdogpolska/poradnia/blob/issue/485/poradnia/letters/tests/messages/surrogates_message.eml

Related issue with full exception: watchdogpolska/poradnia#485

[pfouque]

#164