Now what is you doubt for creating a windows service or how to send e-mail..
1) How to start with windows serviceSimple Windows Service Sample
2) For Sending E-Mail please refer this...How to send A E-Mail From Your web Application...?
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.