1. A method comprising: storing a first set of at least one message at a client system; sending a first request to a server system, said first request including a copy of the first set of messages; and waiting to receive a first response at the client system from the server system, said first response including a first indication of which messages of the first set of messages were received from the client system in the first request, wherein requests and responses are formatted according to a first protocol, said first protocol operative to traverse a firewall.