(SMTP EXCEPTION)The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Must issue a STARTTLS command first. jm5sm6473157pbc.1

protected void btnSendmail_Click(object sender, EventArgs e)
       {
           // System.Web.Mail.SmtpMail.SmtpServer is obsolete in 2.0
           // System.Net.Mail.SmtpClient is the alternate class for this in 2.0
           SmtpClient smtpClient = new SmtpClient();
           MailMessage message = new MailMessage();

           try
           {
               MailAddress fromAddress = new MailAddress(txtEmail.Text, txtName.Text);

               // You can specify the host name or ipaddress of your server
               // Default in IIS will be localhost
               smtpClient.Host = "localhost";

               //Default port will be 25
               smtpClient.Port = 25;
               smtpClient.Host = "smtp.gmail.com";

               //From address will be given as a MailAddress Object
               message.From = fromAddress;

               // To address collection of MailAddress
               message.To.Add("shashik@xxxxx.com");
               message.Subject = "Feedback";

               // CC and BCC optional
               // MailAddressCollection class is used to send the email to various users
               // You can specify Address as new MailAddress("admin1@yoursite.com")
               message.CC.Add("shashik@xxxxx.com");
               //message.CC.Add("admin2@yoursite.com");

                              //Body can be Html or text format
               //Specify true if it  is html message
               message.IsBodyHtml = false;

               // Message body content
               message.Body = txtMessage.Text;



               smtpClient.UseDefaultCredentials=false;
               smtpClient.Credentials = new NetworkCredential("shashixxxx@xxxxx.com", "xxxxxxxxxxxxxx");


               // Send SMTP mail
               smtpClient.Send(message);

               lblStatus.Text = "Email successfully sent.";
           }
           catch (System.Net.Mail.SmtpException ex)
           {
               Response.Write(ex.ToString());
           }
           catch (Exception ex)
           {
               lblStatus.Text = "Send Email Failed.<br>" + ex.Message;
           }
       }</br>