Looking for emailing app

I'm looking for a php application that will allow for emailing to groups of people. For example maybe 100 different people will be managed into 20 different groups. The user would select the group (or multiple groups) and it would query the database to pull all the associated names with these groups, combine into one list and send. Also needed are the user maint screens to manage the changing users and groups. I can write my own, but if there are parts of this application already written and posted somewhere it would give me a moving start. Anyone know of anything like this? Brian