diff --git a/src/Symfony/Component/Notifier/Bridge/Slack/SlackTransport.php b/src/Symfony/Component/Notifier/Bridge/Slack/SlackTransport.php
index 5a98638ab30d5..740a4937ebd6b 100644
--- a/src/Symfony/Component/Notifier/Bridge/Slack/SlackTransport.php
+++ b/src/Symfony/Component/Notifier/Bridge/Slack/SlackTransport.php
@@ -91,6 +91,9 @@ protected function doSend(MessageInterface $message): SentMessage
             throw new TransportException(sprintf('Unable to post the Slack message: "%s".', $result['error']), $response);
         }
 
-        return new SentMessage($message, (string) $this);
+        $sentMessage = new SentMessage($message, (string) $this);
+        $sentMessage->setMessageId($result['ts']);
+
+        return $sentMessage;
     }
 }
diff --git a/src/Symfony/Component/Notifier/Bridge/Slack/Tests/SlackTransportTest.php b/src/Symfony/Component/Notifier/Bridge/Slack/Tests/SlackTransportTest.php
index 3b7a3c6f8ff64..12e00e3f4a951 100644
--- a/src/Symfony/Component/Notifier/Bridge/Slack/Tests/SlackTransportTest.php
+++ b/src/Symfony/Component/Notifier/Bridge/Slack/Tests/SlackTransportTest.php
@@ -110,7 +110,7 @@ public function testSendWithOptions()
 
         $response->expects($this->once())
             ->method('getContent')
-            ->willReturn(json_encode(['ok' => true]));
+            ->willReturn(json_encode(['ok' => true, 'ts' => '1503435956.000247']));
 
         $expectedBody = json_encode(['channel' => $channel, 'text' => $message]);
 
@@ -122,7 +122,9 @@ public function testSendWithOptions()
 
         $transport = $this->createTransport($client, $channel);
 
-        $transport->send(new ChatMessage('testMessage'));
+        $sentMessage = $transport->send(new ChatMessage('testMessage'));
+
+        $this->assertSame('1503435956.000247', $sentMessage->getMessageId());
     }
 
     public function testSendWithNotification()
@@ -138,7 +140,7 @@ public function testSendWithNotification()
 
         $response->expects($this->once())
             ->method('getContent')
-            ->willReturn(json_encode(['ok' => true]));
+            ->willReturn(json_encode(['ok' => true, 'ts' => '1503435956.000247']));
 
         $notification = new Notification($message);
         $chatMessage = ChatMessage::fromNotification($notification);
@@ -158,7 +160,9 @@ public function testSendWithNotification()
 
         $transport = $this->createTransport($client, $channel);
 
-        $transport->send($chatMessage);
+        $sentMessage = $transport->send($chatMessage);
+
+        $this->assertSame('1503435956.000247', $sentMessage->getMessageId());
     }
 
     public function testSendWithInvalidOptions()