Private-Message and Post-Notification Restrictions

[lpetrich]

For suspended users, we at our messageboard would like to restrict private-message and post-notification features in these ways:

• Private messages: they can only send PM's to members of certain usergroups, like the staff ones.
• Post notifications: they can see posts, even in private forums, but they cannot use the post-notification feature for them.

We are still at vB 3.8.4, and it may be that someone has coded add-ons for doing these things. Is anyone willing to try that, or at least give an idea of how feasible it is?

I'm asking about this because I wish to avoid modifying the vB code itself.