// Code by 'dotnetguts at gmail.com'
protected void btnSendEmail_Click(object sender, EventArgs e)
{
//Create Mail Message Object with content that you want to send with mail.
System.Net.Mail.MailMessage MyMailMessage = new System.Net.Mail.MailMessage("dotnetguts@gmail.com","myfriend@yahoo.com",
"This is the mail subject", "Just wanted to say Hello");
MyMailMessage.IsBodyHtml = false;
//Proper Authentication Details need to be passed when sending email from gmail
System.Net.NetworkCredential mailAuthentication = new
System.Net.NetworkCredential("dotnetguts@gmail.com", "myPassword");
//Smtp Mail server of Gmail is "smpt.gmail.com" and it uses port no. 587
//For different server like yahoo this details changes and you can
//get it from respective server.
System.Net.Mail.SmtpClient mailClient = new System.Net.Mail.SmtpClient("smtp.gmail.com",587);
//Enable SSL
mailClient.EnableSsl = true;
mailClient.UseDefaultCredentials = false;
mailClient.Credentials = mailAuthentication;
mailClient.Send(MyMailMessage);
}