jabber:x:expire

This extension is a simple flag identifying that a message has a limited lifetime. If the message is stored offline, the server will not deliver the message and simply delete it after the expiration time has passed. A client may also optionally support removing the message after expiration if it has been received but not yet been viewed. The seconds attribute is always relative to the time in which the message was sent/received (now). The server will adjust the value if it was stored for some time but not expired on the server.

<x xmlns="jabber:x:expire" seconds="3600"/>