Suggestion: Automatically detect and add a label in the Admin Members list for members who are "idle". What that means is:
1. The group has at least one message per month. Otherwise, the group is idle, and there's no need to mark all members.
2. A member is set to No Email, or has been hard bouncing for more than 30 days.
3. If the member is No Email, the member also has no Groups.io web activity in the last 30 days.
This will enable proactive administrators to more easily remove members who "aren't really there" from groups that have membership limits.
There is otherwise no penalty for being "idle", just a label to help owners and moderators keep their membership lists clean if they so choose. If an idle member posts or has web activity, the label is removed.
"Special Notices" members wouldn't get marked idle, even if the group never sends special notices. If an administrator wishes to remove members who are Special Notices only, that can already be easily done.