I think the flaw was mentioned in the first sentence of the parent&#x27;s response: &quot;XMPP lacks a fundamental feature: it does not echo your messages back to your other devices.&quot;  This capability was indeed one of the major selling points of Apple&#x27;s messaging system in the most recent iOS &amp; OS X releases.  If XMPP cannot keep track of multiple clients then that is a huge flaw in todays mobile world.