Raise NotSupportedByMandrillError for unsupported attachment mimetypes.

djrill/mail/backends/djrill.py

@@ -226,6 +226,18 @@ class DjrillBackend(BaseEmailBackend):
         if mimetype is None:
             mimetype = DEFAULT_ATTACHMENT_MIME_TYPE
 
+        # Mandrill silently filters attachments with unsupported mimetypes.
+        # This can be confusing, so we raise an exception instead.
+        (main, sub) = mimetype.lower().split('/')
+        attachment_allowed = (
+            main == 'text' or main == 'image'
+            or (main == 'application' and sub == 'pdf'))
+        if not attachment_allowed:
+            raise NotSupportedByMandrillError(
+                "Invalid attachment mimetype '%s'. Mandrill only supports "
+                "text/*, image/*, and application/pdf attachments."
+                % mimetype)
+
         return {
             'type': mimetype,
             'name': filename or "",

djrill/tests/test_mandrill_send.py

@@ -160,6 +160,24 @@ class DjrillBackendTests(DjrillBackendMockAPITestCase):
             msg="Mandrill API should not be called when send fails silently")
         self.assertEqual(sent, 0)
 
+    def test_attachment_errors(self):
+        # Mandrill silently strips attachments that aren't text/*, image/*,
+        # or application/pdf. We want to alert the Djrill user:
+        with self.assertRaises(NotSupportedByMandrillError):
+            msg = mail.EmailMessage('Subject', 'Body',
+                'from@example.com', ['to@example.com'])
+            # This is the default mimetype, but won't work with Mandrill:
+            msg.attach(content="test", mimetype="application/octet-stream")
+            msg.send()
+
+        with self.assertRaises(NotSupportedByMandrillError):
+            msg = mail.EmailMessage('Subject', 'Body',
+                'from@example.com', ['to@example.com'])
+            # Can't send Office docs, either:
+            msg.attach(filename="presentation.ppt", content="test",
+                mimetype="application/vnd.ms-powerpoint")
+            msg.send()
+
     def test_mandrill_api_failure(self):
         self.mock_post.return_value = self.MockResponse(status_code=400)
         with self.assertRaises(MandrillAPIError):