Need to restrict access

[shipmate]

I need to restrict access to email for most users in my company;

Some users should always have full access to email at all times.
Most other users will need restrictions, such as not sending or recieving any email after 5 pm (internal or external). Although they still might need to access their old messages........

I haven't found a way for Exchange to do this. I also haven't been able to find any 3rd party software to do this either.......it would be nice if it could integrate with active directory, so we restrict via th OU's instead of custom rules, but I'll take any suggestion!

Thanks!