smtplib send_message does not correctly handle unicode addresses if message uses EmailPolicy

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-09-06.18:43:52.220>
labels = ['type-bug', 'expert-email']
title = 'smtplib send_message does not correctly handle unicode addresses if message uses EmailPolicy'
updated_at = <Date 2016-09-06.18:43:52.220>
user = 'https://github.com/bitdancer'

bugs.python.org fields:

activity = <Date 2016-09-06.18:43:52.220>
actor = 'r.david.murray'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2016-09-06.18:43:52.220>
creator = 'r.david.murray'
dependencies = []
files = []
hgrepos = []
issue_num = 27977
keywords = []
message_count = 1.0
messages = ['274597']
nosy_count = 2.0
nosy_names = ['barry', 'r.david.murray']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27977'
versions = ['Python 3.5', 'Python 3.6']