Creating Email Alerts?

Hi,

I am creating a PHP/MySQL driven site, and my client wants to have a user email alert feature that allows users to create date reminders for personal events like birthdays. The user would be able to specify how many days/weeks in advance they would like their email reminder.

I’ve tried to find a tutorial or a starting point on the web, but can’t find anything helpful. Can anyone give me an idea of how this process works, or just point me in the right direction.

I really would appreciate it!