Error When Sending Mail With Asp.net C#

Question

Hello all,

I want to send a mail after my user fill a form but i keep getting the following error "The smtp server requires a secure connection or the client was not authenticated 5.5.1. Authentication required". bellow is my code :

 

int cnt;
       try
       {
           mEmail = Session["mEmail"].ToString();
          // string password = "abraham@2013";
           MailMessage Msg = new MailMessage();
           Msg.From = new MailAddress(mEmail.Trim());
           Msg.To.Add("[email protected]"); // create a frame for HR department
           Msg.Bcc.Add("[email protected]");  //blind copy me
           StreamReader reader = new StreamReader(Server.MapPath("~/SendMail.html"));
           string readFile = reader.ReadToEnd();
           string StrContent = "";
           StrContent = readFile;
           //Here replace the name with [MyName]
           StrContent = StrContent.Replace("[MyName]", lblname.Text);
           string mSubject = "APPLICATION FOR ANNUAL LEAVE";

           StrContent = StrContent.Replace("[subject]", mSubject);
           StrContent = StrContent.Replace("[date1]", txtFromDate.Text.Trim());
           StrContent = StrContent.Replace("[date2]", txtToDate.Text.Trim());
           StrContent = StrContent.Replace("[ddays]",txtNODays.Text.Trim())+" days";
           Msg.Subject = mSubject + " FROM " + lblname.Text;
           Msg.Body = StrContent.ToString();
           Msg.IsBodyHtml = true;
           SmtpClient smtp = new SmtpClient();
           smtp.Host = "smtp.gmail.com"; //"mail.dnextageweb.com";    //
           smtp.Port = 587;
           smtp.EnableSsl = true;
           smtp.Timeout = 40000;
           smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
           smtp.UseDefaultCredentials = false;
           smtp.Credentials = new NetworkCredential("[email protected]", "Delladv!973@");

           smtp.Send(Msg);

           webMessage.Show("Mail sent successful.....");
           return cnt = 1;
       }
       catch (Exception ex)
       {
           webMessage.Show("Error : " + ex.Message.ToString());
           return cnt = -1;
       }