In the directory, because I feel it is probably the easiest area to do this, there should be a box next to the directory email addresses, and once you click that box to check that email along with any other emails you need there should be an email button that will take those email addresses and open the email client with those email addresses.  That way people in the organization can email students, or parents, or even teachers that are not associated via groups or classes but need to receive a communication from a principal or someone else.  

I also think this would be helpful in Rosters area for all groups so that you can truly select the students or parents that you want to email if there are a select few. This would alleviate a lot of email issues and we would have a higher percentage of users logging in and using the system instead of using outside resources.