.eml could not be attached to EmailMessage

[RAMAGE Sébastien]

.eml file could not be attached to EmailMessage using .attach_file() because it raise the following error :
initial_value must be str or None, not bytes

maybe related to mimetype message/rfc822

File "/usr/local/lib/python3.5/dist-packages/django/core/mail/message.py", line 292, in send return self.get_connection(fail_silently).send_messages([self]) 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/backends/smtp.py", line 107, in send_messages sent = self._send(message) 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/backends/smtp.py", line 121, in _send message = email_message.message() 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/message.py", line 256, in message msg = self._create_message(msg) 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/message.py", line 344, in _create_message return self._create_attachments(msg) 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/message.py", line 357, in _create_attachments msg.attach(self._create_attachment(*attachment)) 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/message.py", line 399, in _create_attachment attachment = self._create_mime_attachment(content, mimetype) 
File "/usr/local/lib/python3.5/dist-packages/django/core/mail/message.py", line 380, in _create_mime_attachment content = message_from_string(content) 
File "/usr/lib/python3.5/email/__init__.py", line 38, in message_from_string return Parser(*args, **kws).parsestr(s) 
File "/usr/lib/python3.5/email/parser.py", line 68, in parsestr return self.parse(StringIO(text), headersonly=headersonly) 
TypeError: initial_value must be str or None, not bytes