diff --git a/zerver/lib/outgoing_webhook.py b/zerver/lib/outgoing_webhook.py
index 1292d92768..704c0bd493 100644
--- a/zerver/lib/outgoing_webhook.py
+++ b/zerver/lib/outgoing_webhook.py
@@ -40,9 +40,13 @@ class OutgoingWebhookServiceInterface:
     def process_event(self, event: Dict[Text, Any]) -> Tuple[Dict[str, Any], Any]:
         raise NotImplementedError()
 
-    # Given a successful outgoing webhook REST operation, returns the message
-    # to sent back to the user (or None if no message should be sent).
-    def process_success(self, response: Response, event: Dict[Text, Any]) -> Optional[str]:
+    # Given a successful outgoing webhook REST operation, returns two-element tuple
+    # whose left-hand value contains a success message
+    # to sent back to the user (or None if no success message should be sent)
+    # and right-hand value contains a failure message
+    # to sent back to the user (or None if no failure message should be sent)
+    def process_success(self, response: Response,
+                        event: Dict[Text, Any]) -> Tuple[Optional[str], Optional[str]]:
         raise NotImplementedError()
 
 class GenericOutgoingWebhookService(OutgoingWebhookServiceInterface):
@@ -57,15 +61,16 @@ class GenericOutgoingWebhookService(OutgoingWebhookServiceInterface):
                         "token": self.token}
         return rest_operation, json.dumps(request_data)
 
-    def process_success(self, response: Response, event: Dict[Text, Any]) -> Optional[str]:
+    def process_success(self, response: Response,
+                        event: Dict[Text, Any]) -> Tuple[Optional[str], Optional[str]]:
         response_json = json.loads(response.text)
 
         if "response_not_required" in response_json and response_json['response_not_required']:
-            return None
+            return None, None
         if "response_string" in response_json:
-            return str(response_json['response_string'])
+            return str(response_json['response_string']), None
         else:
-            return None
+            return None, None
 
 class SlackOutgoingWebhookService(OutgoingWebhookServiceInterface):
 
@@ -94,12 +99,13 @@ class SlackOutgoingWebhookService(OutgoingWebhookServiceInterface):
 
         return rest_operation, request_data
 
-    def process_success(self, response: Response, event: Dict[Text, Any]) -> Optional[str]:
+    def process_success(self, response: Response,
+                        event: Dict[Text, Any]) -> Tuple[Optional[str], Optional[str]]:
         response_json = json.loads(response.text)
         if "text" in response_json:
-            return response_json["text"]
+            return response_json["text"], None
         else:
-            return None
+            return None, None
 
 AVAILABLE_OUTGOING_WEBHOOK_INTERFACES = {
     GENERIC_INTERFACE: GenericOutgoingWebhookService,
@@ -228,9 +234,9 @@ def do_rest_call(rest_operation: Dict[str, Any],
     try:
         response = requests.request(http_method, final_url, data=request_data, **request_kwargs)
         if str(response.status_code).startswith('2'):
-            response_message = service_handler.process_success(response, event)
-            if response_message is not None:
-                succeed_with_message(event, response_message)
+            success_message, _ = service_handler.process_success(response, event)
+            if success_message is not None:
+                succeed_with_message(event, success_message)
         else:
             logging.warning("Message %(message_url)s triggered an outgoing webhook, returning status "
                             "code %(status_code)s.\n Content of response (in quotes): \""
diff --git a/zerver/tests/test_outgoing_webhook_interfaces.py b/zerver/tests/test_outgoing_webhook_interfaces.py
index c5412531fa..bcc05fd6a8 100644
--- a/zerver/tests/test_outgoing_webhook_interfaces.py
+++ b/zerver/tests/test_outgoing_webhook_interfaces.py
@@ -36,15 +36,15 @@ class TestGenericOutgoingWebhookService(ZulipTestCase):
     def test_process_success(self) -> None:
         response = mock.Mock(spec=Response)
         response.text = json.dumps({"response_not_required": True})
-        success_response = self.handler.process_success(response, self.event)
+        success_response, _ = self.handler.process_success(response, self.event)
         self.assertEqual(success_response, None)
 
         response.text = json.dumps({"response_string": 'test_content'})
-        success_response = self.handler.process_success(response, self.event)
+        success_response, _ = self.handler.process_success(response, self.event)
         self.assertEqual(success_response, 'test_content')
 
         response.text = json.dumps({})
-        success_response = self.handler.process_success(response, self.event)
+        success_response, _ = self.handler.process_success(response, self.event)
         self.assertEqual(success_response, None)
 
 mock_service = Service()
@@ -95,9 +95,9 @@ class TestSlackOutgoingWebhookService(ZulipTestCase):
     def test_process_success(self) -> None:
         response = mock.Mock(spec=Response)
         response.text = json.dumps({"response_not_required": True})
-        success_response = self.handler.process_success(response, self.event)
+        success_response, _ = self.handler.process_success(response, self.event)
         self.assertEqual(success_response, None)
 
         response.text = json.dumps({"text": 'test_content'})
-        success_response = self.handler.process_success(response, self.event)
+        success_response, _ = self.handler.process_success(response, self.event)
         self.assertEqual(success_response, 'test_content')
diff --git a/zerver/tests/test_outgoing_webhook_system.py b/zerver/tests/test_outgoing_webhook_system.py
index 99a04edeff..69b212494f 100644
--- a/zerver/tests/test_outgoing_webhook_system.py
+++ b/zerver/tests/test_outgoing_webhook_system.py
@@ -27,8 +27,8 @@ def timeout_error(http_method: Any, final_url: Any, data: Any, **request_kwargs:
     raise requests.exceptions.Timeout("Time is up!")
 
 class MockServiceHandler(OutgoingWebhookServiceInterface):
-    def process_success(self, response: Response, event: Dict[Text, Any]) -> Optional[str]:
-        return "Success!"
+    def process_success(self, response: Response, event: Dict[Text, Any]) -> Tuple[Optional[str], Optional[str]]:
+        return "Success!", None
 
 service_handler = MockServiceHandler(None, None, None, None)