Now what is you doubt for creating a windows service or how to send e-mail..
1) How to start with windows service
Simple Windows Service Sample[
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2) For Sending E-Mail please refer this...
How to send A E-Mail From Your web Application...?[
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here in email sending example use your email id came from database...
Now i assume that you can write a code for feting email id from you database so i don't give any idea for that.