Update notice in email sent

api-reference/webhooks/thread-email-sent.mdx

@@ -5,10 +5,11 @@ title: 'Email sent'
 This event is fired when an email is sent in your workspace.
 
 <Warning>
-  An important field that might go unnoticed is `isStartOfThread`. This will tell you if this email
-  is the first message of a thread or not, which is useful if you want to build some auto-reply
-  logic. If you want to build an auto-responder that *only replies* to the first message of a
-  thread, please check [`thread.thread_created`](/api-reference/webhooks/thread-created) instead.
+  An important field that might go unnoticed is `isStartOfThread` which tells you if this email is
+  the first message of a thread or not. This is useful if you want to build some auto-reply logic
+  but note that this will only work for responding to threads received via email. If you want to
+  reply to all threads (including Slack messages and anything received via the API) please check
+  [`thread.thread_created`](/api-reference/webhooks/thread-created) instead.
 </Warning>
 
 ## Schema