Sorry I obviously missed your original message.
> 1) How can the publisher know if the subscriber is getting the data or if
> the max_queued_messages is reached (e.g. the subscriber crashed/is
> restarting/etc) and the previous messages are being dropped? We really
> wouldn't like to implement an application-level flow control, that should
> be preferably handled by the queue.
On a global level you can monitor $SYS/broker/publish/messages/dropped , but you can't do it on a per-client basis.
> 2) Could the broker throttle/stop publishing for channels