Fixed #35365 -- Add RFC 3824 Auto-Submitted header to emails by default

AUTHORS

@@ -192,6 +192,7 @@ answer newbie questions, and generally made Django that much better:
     Can Burak Çilingir <canburak@cs.bilgi.edu.tr>
     Can Sarıgöl <ertugrulsarigol@gmail.com>
     Carl Meyer <carl@oddbird.net>
+    Carter Gracin <carter.rgracin@gmail.com>
     Carles Pina i Estany <carles@pina.cat>
     Carlos Eduardo de Paula <carlosedp@gmail.com>
     Carlos Matías de la Torre <cmdelatorre@gmail.com>

django/core/mail/__init__.py

@@ -13,6 +13,7 @@
     BadHeaderError,
     EmailMessage,
     EmailMultiAlternatives,
+    NoAutoSubmittedHeaderEmailMessage,
     SafeMIMEMultipart,
     SafeMIMEText,
     forbid_multi_line_headers,
@@ -26,6 +27,7 @@
     "DNS_NAME",
     "EmailMessage",
     "EmailMultiAlternatives",
+    "NoAutoSubmittedHeaderEmailMessage",
     "SafeMIMEText",
     "SafeMIMEMultipart",
     "DEFAULT_ATTACHMENT_MIME_TYPE",

django/core/mail/message.py

@@ -280,9 +280,15 @@ def message(self):
         if "message-id" not in header_names:
             # Use cached DNS_NAME for performance
             msg["Message-ID"] = make_msgid(domain=DNS_NAME)
+
+        if "Auto-Submitted" not in self.extra_headers:
+            # Default to adding the Auto-Submitted : auto-generated header
+            self.extra_headers["Auto-Submitted"] = "auto-generated"
+
         for name, value in self.extra_headers.items():
             if name.lower() != "from":  # From is already handled
                 msg[name] = value
+
         return msg
 
     def recipients(self):
@@ -432,6 +438,24 @@ def _set_list_header_if_not_empty(self, msg, header, values):
             msg[header] = value
 
 
+class NoAutoSubmittedHeaderEmailMessage(EmailMessage):
+    """
+    A version of EmailMessage that does not have the default
+    Auto-Submitted : auto-generated header attached to it.
+    """
+
+    def message(self):
+        """
+        This removes the default Auto-Submitted : auto-generated
+        header from the message
+        """
+        msg = super().message()
+        if "Auto-Submitted" in msg:
+            del msg["Auto-Submitted"]
+
+        return msg
+
+
 class EmailMultiAlternatives(EmailMessage):
     """
     A version of EmailMessage that makes it easy to send multipart/alternative

docs/releases/5.1.txt

@@ -193,7 +193,9 @@ Decorators
 Email
 ~~~~~
 
-* ...
+* :class:`<django.core.mail.EmailMessage>` now attaches a default header of "Auto-Submitted : auto-generated"
+  to outgoing emails. You can opt-out of this by using :class:`<django.core.mail.NoAutoSubmittedHeaderEmailMessage>`
+  which does not attach this default header.
 
 Error Reporting
 ~~~~~~~~~~~~~~~

docs/topics/email.txt

@@ -288,7 +288,21 @@ All parameters are optional and can be set at any time prior to calling the
 * ``headers``: A dictionary of extra headers to put on the message. The
   keys are the header name, values are the header values. It's up to the
   caller to ensure header names and values are in the correct format for
-  an email message. The corresponding attribute is ``extra_headers``.
+  an email message. The corresponding attribute is ``extra_headers``. The
+  EmailMessage class attaches a default header of ``Auto-Submitted :
+  auto-generated ``. The sender can opt-out of this default header by using
+  the ``NoAutoSubmittedHeaderEmailMessage`` subclass.
+
+  For example::
+
+    from django.core.mail import NoAutoSubmittedHeaderEmailMessage
+
+    email = NoAutoSubmittedHeaderEmailMessage(
+      "Hello",
+      "Body goes here",
+      "from@example.com",
+      ["to@example.com"]
+    )
 
 * ``cc``: A list or tuple of recipient addresses used in the "Cc" header
   when sending the email.

tests/mail/tests.py

@@ -19,6 +19,7 @@
     DNS_NAME,
     EmailMessage,
     EmailMultiAlternatives,
+    NoAutoSubmittedHeaderEmailMessage,
     mail_admins,
     mail_managers,
     send_mail,
@@ -449,6 +450,18 @@ def test_reply_to_in_headers_only(self):
         ).message()
         self.assertEqual(message["Reply-To"], "reply_to@example.com")
 
+    def test_default_auto_generated_header(self):
+        message = EmailMessage(
+            "Subject", "Content", "from@example.com", ["to@example.com"]
+        ).message()
+        self.assertEqual(message["Auto-Submitted"], "auto-generated")
+
+    def test_no_default_auto_generated_header(self):
+        message = NoAutoSubmittedHeaderEmailMessage(
+            "Subject", "Content", "from@example.com", ["to@example.com"]
+        ).message()
+        self.assertNotIn("Auto-Submitted", message)
+
     def test_multiple_message_call(self):
         """
         Regression for #13259 - Make sure that headers are not changed when