How to activate an email message?

Greetings,

My web app is suppose to send an email to the client two days before a meeting. The email part is taken care of, but what do I do to tell my application that two days before the X date send a message to all the clients with that date? In other words, is there a mechanism that i can use to tell my application to activate a method to send the email?

If someone could help me by providing me direct or indirect feed back, I would greatlly appreciate it.

Thanks,

 Eduardo
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