David one small comment regarding typo in smtplib.py, but most importantly I'd suggest adding additional test case to cover the path (the newly added one) where you get a UnicodeEncodeError upon encoding from or to with UTF8 and then failing to find SMTPUTF8 on the server side. I see we already have test case to cover SMTPNotSupportedError but this covers just the case where the server does not have SMTPUTF8.