Answer:   MailMessage mailMess = new MailMessage ();
mailMess.From = "abc@gmail.com";
mailMess.To = "xyz@gmail.com";
mailMess.Subject = "Test email";
mailMess.Body = "Hi This is a test mail.";
SmtpMail.SmtpServer = "localhost";
SmtpMail.Send (mailMess);
MailMessage and SmtpMail are classes defined System.Web.Mail namespace..

Answer:   SmtpClient smtpClient = new SmtpClient("domain.a2hosted.com", 25);

smtpClient.Credentials = new System.Net.NetworkCredential("user@example.com", "password");
smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;

MailMessage mailMessage = new MailMessage(txtFrom.Text, txtTo.Text);
mailMessage.Subject = txtSubject.Text;
mailMessage.Body = txtBody.Text;
smtpClient.Send(mailMessage);