MailMessage m = new MailMessage();
m.From = new MailAddress("[email protected]", "Your Name");
m.To.Add(new MailAddress("[email protected]", "Recipient Name"));
m.Subject = "Hello";
m.Body = "

My Message

Put the body here.";
m.IsBodyHtml = true;
SmtpClient client = new SmtpClient("smtp.mail.yahoo.com");
client.Send(m);

It was discussed via stackoverflow.
http://stackoverflow.com/questions/684454/how-to-send-mail-from-yahoo-mail-id-in-vb-net-or-c-net-code