Automatic email sending

Hi everyone, my website need to automatically send an email to people when thier account is about to expire, but iam not sure how to do it. In other words its easy to put a check if an account is about to expire and send automatic email when admin logs in to system, but how is it possible to do it in background. -- Murtaza Chang http://dirtinme.blogspot.com/ A Place to throw personal trash http://milddreamerz.blogspot.com For Photoshopers And Digital Art Enthusiasts