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

Backport of 8d789449c7861b8cf8b10d244f26d9d354989aaf from master.

4 files changed, 45 insertions, 6 deletions

diff --git a/django/core/mail/backends/smtp.py b/django/core/mail/backends/smtp.py
index dc6afb0a81..94e3aa1e88 100644
--- a/django/core/mail/backends/smtp.py
+++ b/django/core/mail/backends/smtp.py
@@ -112,7 +112,7 @@ 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
diff --git a/django/core/mail/message.py b/django/core/mail/message.py
index 34caa37ffd..fb15a8c29f 100644
--- a/django/core/mail/message.py
+++ b/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()
 
 
diff --git a/docs/releases/1.7.1.txt b/docs/releases/1.7.1.txt
index dba3ec9f19..3bc15218af 100644
--- a/docs/releases/1.7.1.txt
+++ b/docs/releases/1.7.1.txt
@@ -114,3 +114,5 @@ Bugfixes
   (:ticket:`23609`).
 
 * Fixed generic relations in ``ModelAdmin.list_filter`` (:ticket:`23616`).
+
+* Restored RFC compliance for the SMTP backend on Python 3 (:ticket:`23063`).
diff --git a/tests/mail/tests.py b/tests/mail/tests.py
index 0ea819ffbd..169f9b8fbb 100644
--- a/tests/mail/tests.py
+++ b/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
@@ -984,3 +984,37 @@ class SMTPBackendTests(BaseEmailBackendTests, SimpleTestCase):
         self.assertEqual(myemailbackend.timeout, 42)
         self.assertEqual(myemailbackend.connection.timeout, 42)
         myemailbackend.close()
+
+    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