Comment Re:What's wrong with XMPP, again? (Score 1) 123
You've inadvertently flagged the real problem with XMPP: It doesn't store messages server side, or it does store messages server side, depending on which protocol extensions a given implementation happens to have. For anything that you might want to do with XMPP, there are 2-10 different XEPs with varying levels of support, that describe how to do it.
XMPP badly needed a high-quality reference implementation of a server and a library for implementing clients. Instead it got two crappy reference implementations (that were so bad even the standards editor didn't recommend using them) and a load of partial implementations of the client part of the spec.