email sending issue @yahoo.com on using godaddy.com

Question

string smtphost = "relay-hosting.secureserver.net";

string smtpusername = ConfigurationManager.AppSettings["SMTPUSERNAME"];

string smtppwd = ConfigurationManager.AppSettings["SMTPPASWORD"];

string FromTo = ConfigurationManager.AppSettings["From"];

string From_CC = ConfigurationManager.AppSettings["CC"];

System.Text.StringBuilder strs = new System.Text.StringBuilder();

MailMessage objMail = new MailMessage(FromTo, txtEmail.Text.Trim(), "Welcome", str);

objMail.CC.Add(new MailAddress(From_CC));

objMail.IsBodyHtml = true;

SmtpClient s = new SmtpClient(smtphost);

System.Net.NetworkCredential basicAuthenticationInfo = new System.Net.NetworkCredential(smtpusername, smtppwd);

s.UseDefaultCredentials = false;

s.Credentials = basicAuthenticationInfo;

s.Send(objMail);