importioimportemailimportemail.policyCONTENTS="""From: Nathaniel Borenstein <nsb@bellcore.com>To: Ned Freed <ned@innosoft.com>Subject: Sample messageMIME-Version: 1.0Content-type: multipart/mixed; boundary="i-am-boundary"This is the préamble.  It is to be ignored, though itis a handy place for mail composers to include anexplanatory note to non-MIME compliant readers.--i-am-boundaryContent-type: text/plain; charset=us-asciiThis is explicitly typed plain ASCII text.It DOES end with a linebreak.--i-am-boundaryContent-type: text/plain; charset=utf-8Content-Transfer-Encoding: 8bitThis should be correctly encapsulated: Un petit café ?--i-am-boundary--This is the epilogue.  It is also to be ignored.""".lstrip()CONTENTS_BYTES=io.BytesIO(CONTENTS.encode())# Does not have an impact on the resultPOLICY=email.policy.default.clone(utf8=True)defshow_message(msg):# Parts are correctly decoded in all casesfori,partinenumerate(msg.iter_parts(),1):print(f'MIME PART{i}:')as_string=part.as_string()as_bytes=as_string.encode()print(as_string)as_string=msg.as_string()# When source was bytes, the unicode result of as_string is incorrectas_bytes=as_string.encode()print(as_string)msg_from_binary=email.message_from_binary_file(CONTENTS_BYTES,policy=POLICY)show_message(msg_from_binary)# UnicodeEncodeError: 'utf-8' codec can't encode characters in position 192-193: surrogates not allowed# Using the unicode representation is OK#msg_from_string = email.message_from_string(CONTENTS, EmailMessage)#show_message(msg_from_string)