Not entirely sure how this would work, but if a user is muted and someone sends them a message via /msg send them back a message to say they are muted, so they know they will not respond.
I currently use ChatControl Pro for my /msg if this helps.

This is quite specific. I'm afraid there's no way to reliably handle this within BM, it would need to be added in ChatControl Pro itself.

Thanks, I messaged both of you to figure out which plugin would need to do it.