Rebus can be configured to perform "message auditing", which is the process of taking a copy of all messages. This may sound like a daunting task, but it isn't, because messages can only "disappear" in two places:

1. When they have been properly handled
2. When they have been published and there were 0 subscribers

In general, a publisher does not know the number of subscribers (because the transport might implement multicast natively), so the safe way of auditing messages is to send a copy of

1. each properly handled transport message with the rbs2-audit-reason header set to handled
2. each published transport message with the rbs2-audit-reason header set to published

to the configured audit queue. A few additional headers with audit information will be added to the message copy.

In order to enable message auditing, use the Rebus configuration API like this:

Configure.With(adapter)
    .Transport(t => t.UseMsmq("server.input"))
    .(...)
    .Options(b => b.EnableMessageAuditing("audit@cpvm010"))
    .(...)

in order to send audited messages to the audit queue on the machine cpvm010 (assuming MSMQ here).