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below error is shown when sent the mail

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at 

What I have tried:

I use below code to mail config .thats works in other applications but my application shows the below error how to fix it.

Msg.IsBodyHtml = true;
SmtpClient smtp = new SmtpClient();
smtp.Host = ConfigurationManager.AppSettings["MailServer"];
System.Net.NetworkCredential NetworkCred = new System.Net.NetworkCredential();
Msg.From = new MailAddress(ConfigurationManager.AppSettings["MailFrom"]);
NetworkCred.Password = ConfigurationManager.AppSettings["MailPassword"];
smtp.Credentials = NetworkCred;
smtp.Port = 25;
smtp.EnableSsl = true;

ServicePointManager.ServerCertificateValidationCallback = delegate(object s, System.Security.Cryptography.X509Certificates.X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
return true;

Updated 27-Apr-17 5:55am
F-ES Sitecore 26-Apr-17 11:45am    

smtp.UseDefaultCredentials = false;
smtp.Credentials = NetworkCred;
Andy Lanng 26-Apr-17 12:51pm    
OP gone again? that's why so few solutions highlight O_o
Raja Ganapathy 27-Apr-17 1:25am    
I have use this also but the same error is occurs
David_Wimbley 27-Apr-17 2:33am    
Are you sure the port number is correct? Typically mail servers will have a different SMTP portal for SSL/TLS connections. For example office365 uses port 587.

1 solution

You've set the NetworkCred.Password, but not the NetworkCred.UserName. Most servers will require both a username and a password for authentication.

But there's a better way: put your configuration in the <smtp> Element (Network Settings)[^]:
      <smtp deliveryMethod="network" from="">  

With that in place, you don't need to configure the SmtpClient; the default constructor will automatically read the settings from the config file.
SmtpClient smtp = new SmtpClient();
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