using System;
using System.Web.Mail;
...
protected void Button1_Click(object sender, EventArgs e)
{
string fromAddress = "asp@asp.net";
string fromName = "Kerem Kosaner";
string toAddress = "asp@asp.com";
string toName = "Kerem Kosaner";
string msgSubject = "E-Mail";
string msgBody = "Hello";

MailMessage Message = new MailMessage();
Message.To = toAddress;
Message.From = fromAddress;
Message.Subject = msgSubject;
Message.Body = msgBody;
SmtpMail.SmtpServer = "your mail server name goes here";
SmtpMail.Send(Message);
}