Help creating a Delivery Status Notification using email library module

Python Help
1

I’m trying to create a DSN (also known as a Non-Delivery Report) using the email library module.

I create a new message and add 3 attachments. When I try to print the resulting email, I get this error:

Traceback (most recent call last):
  File "/home/mgrant/./send-dsn.py", line 97, in <module>
    print(dsn)
  File "/usr/lib/python3.9/email/message.py", line 971, in __str__
    return self.as_string(policy=self.policy.clone(utf8=True))
  File "/usr/lib/python3.9/email/message.py", line 968, in as_string
    return super().as_string(unixfrom, maxheaderlen, policy)
  File "/usr/lib/python3.9/email/message.py", line 158, in as_string
    g.flatten(self, unixfrom=unixfrom)
  File "/usr/lib/python3.9/email/generator.py", line 116, in flatten
    self._write(msg)
  File "/usr/lib/python3.9/email/generator.py", line 181, in _write
    self._dispatch(msg)
  File "/usr/lib/python3.9/email/generator.py", line 218, in _dispatch
    meth(msg)
  File "/usr/lib/python3.9/email/generator.py", line 276, in _handle_multipart
    g.flatten(part, unixfrom=False, linesep=self._NL)
  File "/usr/lib/python3.9/email/generator.py", line 116, in flatten
    self._write(msg)
  File "/usr/lib/python3.9/email/generator.py", line 181, in _write
    self._dispatch(msg)
  File "/usr/lib/python3.9/email/generator.py", line 218, in _dispatch
    meth(msg)
  File "/usr/lib/python3.9/email/generator.py", line 335, in _handle_message_delivery_status
    g.flatten(part, unixfrom=False, linesep=self._NL)
  File "/usr/lib/python3.9/email/generator.py", line 107, in flatten
    old_msg_policy = msg.policy
AttributeError: 'str' object has no attribute 'policy'

I’ve narrowed this down to the second attachment which I create as follows:

msg.add_attachment("""\
Reporting-MTA: dns; {}

Original-Recipient: rfc822;{}
Final-Recipient: rfc822;{}
Action: failed
Status: 5.7.1
Diagnostic-Code: smtp; 571 Delivery not authorized, message refused
Last-Attempt-Date: {}
""".format(domain, recipient, recipient, received).encode('us-ascii'),
                   maintype="message",
                   subtype="delivery-status",
                   cte=None)

If I change the maintype to “text” and subtype to “plain”, the message prints out, but with the incorrect content-type for that part. The message/delivery-status causes it to call _handle_message_delivery_status() in generator.py. I’m starting to wonder if there’s a bug in there, but equally, I’m not convinced I’m doing this correctly.

In _handle_message_delivery_status() in generator.py, there is this loop:

        for part in msg.get_payload():
            s = self._new_buffer()
            g = self.clone(s)
=>          g.flatten(part, unixfrom=False, linesep=self._NL)
...

msg.get_payload() is returning the entire string which I formatted in my attachment above, for example:

(Pdb) msg.get_payload()
'Reporting-MTA: dns; example.com\n\nOriginal-Recipient: rfc822;joe.user@example.com\nFinal-Recipient: rfc822;joe.user@example.com\nAction: failed\nStatus: 5.7.1\nDiagnostic-Code: smtp; 571 Delivery not authorized, message refused\nLast-Attempt-Date: Thu, 05 May 2022 18:54:51 -0000\n'

Hence the for loop, part gets each character of this in form of a string starting with ‘R’, clearly this isn’t what that loop is expecting!

Is this a bug in _handle_message_delivery_status()? or am I not creating this body part attachment correctly?

2

Not to detract, but if you can use Sendgrid - I would use it. It has a python library too.

3

Sendgrid? as in the paid service to send email? I’m completely confused as to why this might be helpful. I’m developing something in Python, it’s sending and receiving emails.

4

Sendgrid has a free tier. Sendgrid is just a very streamlined solution for sending email via Python and PowerShell. They have a web API and SMTP servers.

I guess I didn’t realize you needed to receive them.

You may check Github Issues page if there is one.

5

I had the exact same issue, I ended up using the old MIMEMultipart object to create the message.

Here is the code, it is a bit more general than just sending DSN’s.

class Part(BaseModel):
    body: str
    content_type: tuple[str, str]

class Email(BaseModel):
    from_: EmailStr = Field(..., alias="from")
    to: EmailStr | list[EmailStr]
    subject: str
    body: str
    headers: Optional[dict[str, str]]
    parts: Optional[list[Part]]
    html: Optional[bool] = False

def create_message(email: Email):
    msg = MIMEMultipart()
    msg["Subject"] = email.subject
    msg["From"] = email.from_
    msg["To"] = email.to if not isinstance(email.to, list) else ",".join(email.to)
    if email.headers is not None:
        for header_name, header_value in email.headers.items():
            msg[header_name] = header_value

    body = MIMEText(email.body, _subtype="html" if email.html else "plain")

    parts: list = [body]

    if email.parts:
        for part in email.parts:
            m = Message()
            m.set_payload(part.body)
            subpart = MIMEMessage(m, _subtype=part.content_type[1])
            parts.append(subpart)

    msg.set_payload(parts)
    return msg
6

I managed to get around this by setting the policy and passing a contentmanager arg (I just passed the raw_data_manager from the email.contentmanager package) like this:

from email.policy import default
from email import policy
from email.mime.text import MIMEText
from email.headerregistry import ContentTypeHeader

then, when I create the DSN:

dsn = EmailMessage()
dsn.policy = policy.SMTP
dsn.make_mixed()

dsn.add_attachment("""\
Reporting-MTA: dns; {}

Original-Recipient: rfc822;{}
Final-Recipient: rfc822;{}
Action: failed
Status: 5.7.1
Diagnostic-Code: smtp; 571 Delivery not authorized, message refused
Last-Attempt-Date: {}
""".format(domain, recipient, recipient, received).encode("ascii"),
                   maintype="report-type",
                   subtype="delivery-status",
                   content_manager=email.contentmanager.raw_data_manager,
                   cte='7bit')
7

Hi Michael,

I do need something similar. Have you made this library public? if so please share.

Thanks

8

The email library is part of python. The code here is an example to use it. There is nothing more to make public, just use it like the example given.