ASP Birthday Greeting Script

I'm working on a an ASP script that should be able to send Birthday greetings to the employees in the company. But I was thinking of a way to invoke the script everyday at 9 AM to send the email if it matches any of the birth dates in the database.

One way I thought about was keeping the browser window open on a server and create a rule which refreshes the script everyday at 9 AM, but thought that this way might not be very effective especially if someone closed the window.