Attaching email file to email fails if the attachment is using 8bit Content-Transfer-Encoding

[Trenton H]

If the attached email file is attached to an email, such as the code snipped below, the sending will fail due to the presence of non-ASCII content in the attachment.

email = EmailMessage(
    subject="subject",
    body="body",
    to="someone@somewhere.com",
)
email.attach_file(original_file)
n_messages = email.send()

Traceback (most recent call last):
  File "/usr/src/paperless/src/documents/signals/handlers.py", line 989, in email_action
    n_messages = email.send()
                 ^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/core/mail/message.py", line 301, in send
    return self.get_connection(fail_silently).send_messages([self])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/core/mail/backends/smtp.py", line 136, in send_messages
    sent = self._send(message)
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/core/mail/backends/smtp.py", line 156, in _send
    from_email, recipients, message.as_bytes(linesep="\r\n")
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/core/mail/message.py", line 148, in as_bytes
    g.flatten(self, unixfrom=unixfrom, linesep=linesep)
  File "/usr/local/lib/python3.12/email/generator.py", line 117, in flatten
    self._write(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 182, in _write
    self._dispatch(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 219, in _dispatch
    meth(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 286, in _handle_multipart
    g.flatten(part, unixfrom=False, linesep=self._NL)
  File "/usr/local/lib/python3.12/email/generator.py", line 117, in flatten
    self._write(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 182, in _write
    self._dispatch(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 219, in _dispatch
    meth(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 372, in _handle_message
    g.flatten(msg.get_payload(0), unixfrom=False, linesep=self._NL)
  File "/usr/local/lib/python3.12/email/generator.py", line 117, in flatten
    self._write(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 182, in _write
    self._dispatch(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 219, in _dispatch
    meth(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 446, in _handle_text
    super(BytesGenerator,self)._handle_text(msg)
  File "/usr/local/lib/python3.12/email/generator.py", line 263, in _handle_text
    self._write_lines(payload)
  File "/usr/local/lib/python3.12/email/generator.py", line 156, in _write_lines
    self.write(line)
  File "/usr/local/lib/python3.12/email/generator.py", line 420, in write
    self._fp.write(s.encode('ascii', 'surrogateescape'))

                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 UnicodeEncodeError: 'ascii' codec can't encode characters in position 10-15: ordinal not in range(128)

[Tim Graham]

Trenton, It would be helpful if you could provide some more information about this because I'm not sure we have any triagers who are experts in this area. Where is Django at fault and how can we fix it?