IQ messages are "guaranteed" at the protocol level. E.g. recipient is required by the protocol to reply, so pretty much all XMPP libraries make it easy to hand

IQ messages are "guaranteed" at the protocol level. E.g. recipient is required by the protocol to reply, so pretty much all XMPP libraries make it easy to handle an IQ send with a reply timeout. This is not quite the same as "guaranteed delivery" but if you get a reply for your IQ you know it was received. So XMPP gives you request/reply as well as one-way fire-and-forget semantics. This, in conjunction with presence (so I have a good idea if recipient is currently online) give fairly strong toolkit for reliable M2M messaging.