using System.Net.Mail;
SmtpClient obj = new SmtpClient();
MailMessage Mailmsg = new MailMessage();
Mailmsg.To.Clear();
Mailmsg.To.Add(new MailAddress(sectionEmail.SelectedValue.ToString()));
Mailmsg.From = new MailAddress("sender mail");
Mailmsg.Subject = "";
Mailmsg.BodyEncoding = System.Text.Encoding.UTF8;
Mailmsg.IsBodyHtml = true;
obj.Host = "your host";
System.Net.NetworkCredential basicAuthenticationInfo = new System.Net.NetworkCredential("sender mail", "mail password");
obj.UseDefaultCredentials = false;
obj.Credentials = basicAuthenticationInfo;
Mailmsg.Body = TextBox1.Text;
Mailmsg.IsBodyHtml = true;
try
{
obj.Send(Mailmsg);
}
catch (Exception ex)
{
}