With a little more investigation with Felu we have come accross that
Preferences > Customize > Event Notifications > Show Messenger Plus pop-up notifications when Busy
governs all of the toast that are generated apart from the email notifications (well there may be more but this is at least one of them
). So shouldn't they use the same function as the others when generated and be subject to the same conditions such as when busy? Maybe also it might be nice if there was a global setting but then each of the individual Event Notifications could be modified (but still use the global settings for scripts as a nice thing to do
). It was just a thought.