I'm basically looking for a program/app/script (can be commercial) which I can ideally install on a windows server (we can run asp, asp.net php mssql) 

we have different groups of people who send newsletters to web members, I want to bring it all into one app which I can monitor and control. Ideally it would be able to create html newsletters, (with some templates) track emails and click throughs. Manage email lists subscribe/unsubscribes. And importantly have different levels of admin, so a newsletter creator could log in and create and send off an email, it goes into a queue where a communications editor can have an overview of all newsletters and approve the sending of the emails or edit them before they are sent off. 

before I start coding something up myself I thought I'd ask if anyone has any advice!

Cheers!