How to send mail automatically if Date expires

In our application if some one purchase a tool for and if the license provided is开发者_开发技巧 for some few days (suppose for a week or an year).. How to send a mail automatically to the ID given by him before a day or a few days .. If any one having worked out means it will be very helpful to me...

Thanks & Regards, Dorababu

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I assume this subscriber information is being kept in a database somewhere? How about a small console app that's scheduled to run every day which polls the data and looks for subscribers that are soon to expire? Than just have that app send out some email reminder to the customer.

If this isn't what you're talking about, please elaborate. The question is a bit unclear.