Email reminder script

I need a web script creating that will do the following:

* Has a form on the front end that website visitors fill in with their name, email, a date and a message.

* When the user submits the form the data must be held until the selected date is due

* When the date is due, the script must look up a html and text version of an email template saved on the server

* The message and name parts that were filled in on the form must be populated within the html and text versions of the email so that when they are sent they are personalised to the users details.

* The subject line of the email must also be personalised with the name field from the form

* Once the email has been personalised with the details from the form, it must be sent to the email address the person entered on the form


Additional features
* The ability for people to set recurring email reminders or simply a reminder by date
* The ability for people to stop receiving the emails - unsubscribe
* The ability for admin to search all past, present and future emails to be sent
* If people unsubscribe it is only from 1 email and not all emails


Requirements
* I will need a detailed explanation of how you plan to achieve this task
* The system will need to be secure from any types of malicious attacks
* The system must be highly scalable