How to send Email

 Hello all,
Once again for one important point i need help
i am using following code to send email
  MailMessage message = new MailMessage();
        message.To = "srankamal@gmail.com";
        message.From = "srankamal@gmail.com";
        message.Body = body;
       SmtpMail.Send(message);               
       

 i want to set a condition to send email :
1)User shall be able to specify the  number of days to include like want to send email on 25th feb as today 21st feb.

2)automated  process  to  send email  alerts  at  user  defined times, i.e. ...