The email backend might be quite a heavy-weight idea ... although I think it would do the job if properly setup and _very_ reliably. I was thinking about something similar to google pub/sub.
Another approach how to add reliability to the current fedmsg would be to add an optional sqlite persistence to each application publishing the fedmsg messages. Basically, the messages would be stored in a circular buffer of configurable size so that when some service drops off, we could still keep messages for it for some time until it recovers. This is a very rough idea and there is this whole problem how subscribes should get information about providers and so on...some analysis is here http://fedmsg.com/federated-message-bus/ I would like to continue the fedmsg project that was mainly started by Ralph Bean some years ago because I like the idea of a federated distribution-independent message bus that was triggered by Debian/Fedora cooperation. There might be some technical challenges on the way but solvable in the end and the solution might be interesting. On the other hand, I am only one guy with limited time so if anyone wants to cooperate on this, it would be most welcome. clime