After reading https://ring.cx/en/about/technical#OpenDHT and https://tuleap.ring.cx/plugins/tracker/?aid=765 I think I know how it is supposed to work at the moment;Offilne messaging works only with text messages (of some size xxx bytes?) If the recipient is offline, the message is stored for 5 minutes in DHT (Distributed Hash Table) that the networked hosts share together If the recipient does not come online in 5 minutes, the message timeouts and never reaches the recipient This happens also if the sender is on-line all the time, (which is a bug IMHO...)