email alert for contract expiry

Dear Sir,

i need formula & macro to send email from excel.

if contract is valid then in B7 it show for how many days remaing for expiry. and if expired then it will show it expired

also same time from 15 days before excell will start sending email as per mail id mentioned G3, G4, G5. and as per below schedule.

email on 15 days before
email on 13 days before
email on 10 days before
email on 7 days before
email on 4 days before
email on 3 days before
email on 1 day before
email on on expiry date
stop
sample workbook attached

thank you,
Shailesh