Hi
Try this
In below gridview u need to add checkbox,then only u use gridview.selecteitems
foreach (GridDataItem gdi in usersGridView.SelectedItems) {
HostAdd = ConfigurationManager.AppSettings["Host"].ToString();
FromEmailid = ConfigurationManager.AppSettings["FromMail"].ToString();
Pass = ConfigurationManager.AppSettings["Password"].ToString();
Label LblName = gr.FindControl("LblName") as Label;
Label LblMail = gr.FindControl("LblEmail") as Label;
string Name = LblName.Text;
string Mail = LblMail.Text;
string subject = TxtSubject.Text;
SmtpClient client = new SmtpClient();
MailMessage msg = new MailMessage();
NetworkCredential credentials = new NetworkCredential(FromEmailid, Pass);
client.Host = HostAdd;
client.Port = 25;
client.UseDefaultCredentials = false;
client.Credentials = credentials;
client.EnableSsl = true;
MailAddress from = new MailAddress(FromEmailid);
msg.IsBodyHtml = true;
msg.Subject = subject;
msg.Body = ReadTemplate(Name);
msg.To.Add(Mail);
msg.From = from;
client.Send(msg);
LblMessage.Text = "Email Send Successfully";
LblMessage.Visible = true;
}