Richard,
Group members only mute receipt in their own mailbox. It does not affect delivery to other members nor does it stop the appearance of the topic or posts on the group site. It allows members to manage the flow of email to their inbox.
I do suggest you disallow ¡°no mail¡± as an option, if you haven¡¯t already done so. I have also set groups I started to the options that send only the first email in a thread and then allow members to opt into (¡°follow¡±) a topic.
Frances
Frances