The transitions of a message between the actor and the dependent is
Actor sends the message to Dependent, or fails to send it.
Dependent receives the message, or fails to receive it.
Dependent responds with a response-message to the received-message, or fails to respond.
Actor receives the response-message, or fails to receive it.
We can symbolize these statuses as
A display for showing details of actors, messages, and listeners (dependents) might be
Each message is given a row and the delivery and response status is detailed for each listener. My bare tabular example would have much more detail on it in practice. This is not a overview display and so concerns with overwhelming the user with too much detail is not of relevance. If you only have to show a few listeners and perhaps a brief time window of messages this display will quickly show specific problem with delivery and response.
Inverting and aggregating the above example leads to the tighter display
We are, again, showing each message, but the columns now indicate how many listeners are in each of the delivery or response states.
Lastly, as everyone loves a set of small multiples graphs here is 40 minutes of activity and status where the green line is the number of listeners, the black lines show positive trends and the red negative ones.
Man, that is an ugly chart (and is playing loose with small multiples).