Fixed #23063 -- Convert \n and \r to \r\n when using the SMTP backend as per RFC.

django/core/mail/backends/smtp.py

@@ -120,7 +120,7 @@ class EmailBackend(BaseEmailBackend):
                       for addr in email_message.recipients()]
         message = email_message.message()
         try:
-            self.connection.sendmail(from_email, recipients, message.as_bytes())
+            self.connection.sendmail(from_email, recipients, message.as_bytes(linesep='\r\n'))
         except smtplib.SMTPException:
             if not self.fail_silently:
                 raise

django/core/mail/message.py

@@ -123,7 +123,7 @@ def sanitize_address(addr, encoding):
 
 
 class MIMEMixin():
-    def as_string(self, unixfrom=False):
+    def as_string(self, unixfrom=False, linesep='\n'):
         """Return the entire formatted message as a string.
         Optional `unixfrom' when True, means include the Unix From_ envelope
         header.
@@ -133,13 +133,16 @@ class MIMEMixin():
         """
         fp = six.StringIO()
         g = generator.Generator(fp, mangle_from_=False)
-        g.flatten(self, unixfrom=unixfrom)
+        if six.PY2:
+            g.flatten(self, unixfrom=unixfrom)
+        else:
+            g.flatten(self, unixfrom=unixfrom, linesep=linesep)
         return fp.getvalue()
 
     if six.PY2:
         as_bytes = as_string
     else:
-        def as_bytes(self, unixfrom=False):
+        def as_bytes(self, unixfrom=False, linesep='\n'):
             """Return the entire formatted message as bytes.
             Optional `unixfrom' when True, means include the Unix From_ envelope
             header.
@@ -149,7 +152,7 @@ class MIMEMixin():
             """
             fp = six.BytesIO()
             g = generator.BytesGenerator(fp, mangle_from_=False)
-            g.flatten(self, unixfrom=unixfrom)
+            g.flatten(self, unixfrom=unixfrom, linesep=linesep)
             return fp.getvalue()
 
 

docs/releases/1.7.1.txt

@@ -115,3 +115,5 @@ Bugfixes
   (:ticket:`23609`).
 
 * Fixed generic relations in ``ModelAdmin.list_filter`` (:ticket:`23616`).
+
+* Restored RFC compliance for the SMTP backend on Python 3 (:ticket:`23063`).

tests/mail/tests.py

@@ -9,7 +9,7 @@ import smtpd
 import sys
 import tempfile
 import threading
-from smtplib import SMTPException
+from smtplib import SMTPException, SMTP
 from ssl import SSLError
 
 from django.core import mail
@@ -1038,3 +1038,37 @@ class SMTPBackendTests(BaseEmailBackendTests, SimpleTestCase):
     def test_email_timeout_override_settings(self):
         backend = smtp.EmailBackend()
         self.assertEqual(backend.timeout, 10)
+
+    def test_email_msg_uses_crlf(self):
+        """#23063 -- Test that RFC-compliant messages are sent over SMTP."""
+        send = SMTP.send
+        try:
+            smtp_messages = []
+
+            def mock_send(self, s):
+                smtp_messages.append(s)
+                return send(self, s)
+
+            SMTP.send = mock_send
+
+            email = EmailMessage('Subject', 'Content', 'from@example.com', ['to@example.com'])
+            mail.get_connection().send_messages([email])
+
+            # Find the actual message
+            msg = None
+            for i, m in enumerate(smtp_messages):
+                if m[:4] == 'data':
+                    msg = smtp_messages[i+1]
+                    break
+
+            self.assertTrue(msg)
+
+            if PY3:
+                msg = msg.decode('utf-8')
+            # Ensure that the message only contains CRLF and not combinations of CRLF, LF, and CR.
+            msg = msg.replace('\r\n', '')
+            self.assertNotIn('\r', msg)
+            self.assertNotIn('\n', msg)
+
+        finally:
+            SMTP.send = send