Custom email program to schedule sending emails

Our client has 2800 sales agents, and wants an email program that will: * send a form letter out on a particular date including the agent's name/address information. * offers multiple form letters, on various topics * each subscriber email would have its own dates for each form letter * send emails as a batch daily at a time selectable by me * each dealer to get their own login/password to add their own subscriber emails with send dates and form selection * MySQL based linux server (Plesk) altho I'd prefer something that runs independent of the control panel * should be insertable into a html template (can call php pages as needed) * Bonus if subscribers could have an area to subscribe/unsubscribe themselves Please advise cost and turnaround time. The interface itself does not need to be anything fancy, just easy to follow. White background, we will insert it into our template. Thanks