Can a List - User field also show groups?

I have a messages table in my app. RIght now the Recipients field is just a list of users. But those users are all part of departments. Is it possible for the fields to contain both users and groups? Example the field would be a check box of users and groups:

John Smith
Jane Doe
Ed Ward
Marketing Department
Finance Department

So if I want to Email John Smith and the Finance Department, I can check them off and do so.

Thanks! Pat