Automated Reminder Script

Hello, I need someone for a very small project. I have an appointment website and I would like to implement a reminder function i.e. few days before the appointment date, the user receives an reminding e-mail. Currently, all the appointments are recorded in a table of the database. The table includes all the required information : id / user / email / appointment date / appointment time / id of the professional with who the appointment was taken with. The script needs to send an e-mail a 31, 14, 7 and 1 days before the appointment date. The e-mail send needs to include - some text, - the date and time of the appointment, - the name and address of the professional (these information are into another table of the same database). Many thanks, Thibaud