Make sure that there is a to address in the message

The first one in the list of recipients is the to address. The rest
of recipients are sent as Bcc

diffengine/sendgrid.py

@@ -31,7 +31,7 @@ def mailer(self, api_token):
 
     def build_recipients(self, recipients):
         if recipients:
-            return [Bcc(x.strip()) for x in recipients.split(",")]
+            return [x.strip() for x in recipients.split(",")]
 
     def build_subject(self, diff):
         return diff.old.title

test_diffengine.py

@@ -377,7 +377,7 @@ def test_do_mail_if_entry_has_diff(self):
         sendgrid_config = {
             "api_token": "12345",
             "sender": "[email protected]",
-            "recipients": "[email protected], [email protected]",
+            "recipients": "[email protected]",
         }
         result = process_entry(entry, {"sendgrid": sendgrid_config}, None, sendgrid)
 
@@ -639,6 +639,26 @@ def test_raises_if_not_all_archive_urls_are_present(self):
                 "sendgrid.publish_diff raised AchiveUrlNotFoundError unexpectedly!"
             )
 
+    def test_only_one_recipient(self):
+        config = {
+            "sendgrid": {
+                "api_token": "12345",
+                "sender": "[email protected]",
+                "recipients": "[email protected]",
+            }
+        }
+
+        sendgrid = SendgridHandler(config["sendgrid"])
+
+        diff = get_mocked_diff(False)
+        type(diff.old).archive_url = PropertyMock(return_value="http://test.url/old")
+        type(diff.new).archive_url = PropertyMock(return_value="http://test.url/new")
+
+        try:
+            sendgrid.publish_diff(diff, config["sendgrid"])
+        except Exception as e:
+            self.fail(e)
+
 
 def get_mocked_diff(with_archive_urls=True):
     old = MagicMock()