Comment by hengheng

If you're talking about Multi-User Chats, then on entering a room the server should send previous messages (http://xmpp.org/extensions/xep-0045.html#enter-history), with no requirements set in stone (except when the client specifies a maximum amoun to send).

When a client logs in, it is true that a server doesn't have to send messages back, but that's the goal of XEP-0313.

There was certain controversy about which protocol to use for sharing history between clients for both private chats and MUC, but now XEP0313 seems to be the future of it.

http://stackoverflow.com/questions/25982426/persistent-xmpp-...

There are implementations for servers, e.g https://code.google.com/p/prosody-modules/wiki/mod_mam_muc, but I have yet to see a client reliably supporting this.

I haven't heard of an extension that does that either, but I'm not sure that would scale well for busy long-running Multi User Chats.

But the benefit of XMPP is that a new extension can be proposed that does this if enough people want such a feature. Personally I would argue that a better approach would be to make Public MUC logs accessible and searchable via a web interface and to have the client log chats going forward from when they join (with offline messaging from the server so you don't have to be online the whole time).