Add Auto-Submitted header

Recommended by RFC 3834.

issue6673
review35211002

notification.py

@@ -177,6 +177,7 @@ class Email(ModelSQL, ModelView):
         msg['Cc'] = ', '.join(cc)
         msg['Bcc'] = ', '.join(bcc)
         msg['Subject'] = Header(title, 'utf-8')
+        msg['Auto-Submitted'] = 'auto-generated'
         return msg
 
     def get_log(self, record, trigger, msg):

tests/test_notification_email.py

@@ -94,6 +94,7 @@ class NotificationEmailTestCase(ModuleTestCase):
             self.assertEqual(msg['From'], FROM)
             self.assertEqual(msg['Subject'], 'Notification Email')
             self.assertEqual(msg['To'], 'Administrator <user@example.com>')
+            self.assertEqual(msg['Auto-Submitted'], 'auto-generated')
             self.assertEqual(msg.get_content_type(), 'multipart/alternative')
             self.assertEqual(
                 msg.get_payload(0).get_payload(), 'Hello Michael Scott')