Detecting if an email is a “Delivery Status Notification” and extract information - Python

Question

I\'m using the Python email module to parse emails.

I need to be able to tell if an email is a \"Delivery Status Notification\", find out what the status is

Answer 1

The docs you cited says that the message is multi-part if it is DSN:

import email

msg = email.message_from_string(emailstr)

if (msg.is_multipart() and len(msg.get_payload()) > 1 and 
    msg.get_payload(1).get_content_type() == 'message/delivery-status'):
    # email is DSN
    print(msg.get_payload(0).get_payload()) # human-readable section

    for dsn in msg.get_payload(1).get_payload():
        print('action: %s' % dsn['action']) # e.g., "failed", "delivered"

    if len(msg.get_payload()) > 2:
        print(msg.get_payload(2)) # original message

Format of a Delivery Status Notification (from rfc 3464):

A DSN is a MIME message with a top-level content-type of
multipart/report (defined in [REPORT]).  When a multipart/report
content is used to transmit a DSN:

(a) The report-type parameter of the multipart/report content is
    "delivery-status".

(b) The first component of the multipart/report contains a human-
    readable explanation of the DSN, as described in [REPORT].

(c) The second component of the multipart/report is of content-type
    message/delivery-status, described in section 2.1 of this
    document.

(d) If the original message or a portion of the message is to be
    returned to the sender, it appears as the third component of the
    multipart/report.

Answer 2

I don't use Python but I suppose Gmail improved its support to DSN because my tests are successfull:

You can see in the sample below this is a multipart message with "Content-Type: multipart/report; report-type=delivery-status".

The way I identify reliably that it is a DSN:

• The first row is "Return-path: <>"
• Content-Type is "multipart/report" with "report-type=delivery-status"

Then, I know that:

• The report content is in the part with Content-Type = "message/delivery-status"
• Status and Action fields are always present in the report content.
• Note the Status field can be less precise than other status eventually present in the Diagnostic-Code field (not mandatory). However, the sample below is good (same status in all fields)
• The original message is in the part with Content-Type = "message/rfc822". Sometimes, MTA returns only original message headers without content. In this case, Content-Type is "text/rfc822-headers".

Sample DSN received after an e-mail sent to test-dsn-failure@gmail.com:

Return-path: <>
Received: from xxx ([xxx])
    by xxx with ESMTP; Fri, 04 May 2012 16:18:13 +0200
From: <Mailer-Daemon@xxx> (Mail Delivery System)
To: xxx
Subject: Undelivered Mail Returned to Sender
Date: Fri, 04 May 2012 15:25:09 +0200
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
 boundary="HTB3nt3RR7vw/QMPR4kDPbKg+XWjXIKdC/rfHQ=="

This is a MIME-encapsulated message.

--HTB3nt3RR7vw/QMPR4kDPbKg+XWjXIKdC/rfHQ==
Content-Description: Notification
Content-Type: text/plain

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to <postmaster@xxx>

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

<test-dsn-failure@gmail.com>: 550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596 t12si10077186weq.36


--HTB3nt3RR7vw/QMPR4kDPbKg+XWjXIKdC/rfHQ==
Content-Description: Delivery report
Content-Type: message/delivery-status

Reporting-MTA: dns; xxx
Arrival-Date: Fri, 04 May 2012 15:25:09 +0200

Final-Recipient: rfc822; test-dsn-failure@gmail.com
Status: 5.1.1
Action: failed
Last-Attempt-Date: Fri, 04 May 2012 15:25:09 +0200
Diagnostic-Code: smtp; 550-5.1.1 The email account that you tried to reach does not exist. Please try
550-5.1.1 double-checking the recipient's email address for typos or
550-5.1.1 unnecessary spaces. Learn more at
550 5.1.1 http://support.google.com/mail/bin/answer.py?answer=6596 t12si10077186weq.36

--HTB3nt3RR7vw/QMPR4kDPbKg+XWjXIKdC/rfHQ==
Content-Description: Undelivered Message
Content-Type: message/rfc822

[original message...]

Answer 3

The X-Failed-Recipients header seems to be the quickest way to identify gmail DSN. After that, it seems you must parse the text/plain content.