c# SmtpClient class not able to send email using gmail

Question

I'm having trouble sending email using my gmail account. Im pulling my hair out.

The same settings work fine in Thunderbird.

Here's the code. I've also tried port 465 with no luck.

SmtpClient ss = new SmtpClient("smtp.gmail.com", 587); ss.Credentials = new NetworkCredential("username", "pass"); ss.EnableSsl = true; ss.Timeout = 10000; ss.DeliveryMethod = SmtpDeliveryMethod.Network; ss.UseDefaultCredentials = false;  MailMessage mm = new MailMessage("[email protected]", "[email protected]", "subject here", "my body"); mm.BodyEncoding = UTF8Encoding.UTF8; mm.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure; ss.Send(mm); 

Heres the error

"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 "

Heres the stack trace

   at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response)    at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, String from)    at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception)    at System.Net.Mail.SmtpClient.Send(MailMessage message)    at email_example.Program.Main(String[] args) in C:\Users\Vince\Documents\Visual Studio 2008\Projects\email example\email example\Program.cs:line 23    at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)    at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)    at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()    at System.Threading.ThreadHelper.ThreadStart_Context(Object state)    at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)    at System.Threading.ThreadHelper.ThreadStart() 

Answer 1

You won't belive what fixed my problem.

The Credentials property

ss.Credentials = new NetworkCredential("username", "pass"); 

must be declared after

ss.UseDefaultCredentials = false; 

So the final working code listing is

SmtpClient ss = new SmtpClient("smtp.gmail.com", 587); ss.EnableSsl = true; ss.Timeout = 10000; ss.DeliveryMethod = SmtpDeliveryMethod.Network; ss.UseDefaultCredentials = false; ss.Credentials = new NetworkCredential("username", "pass");  MailMessage mm = new MailMessage("[email protected]", "[email protected]", "subject here", "my body"); mm.BodyEncoding = UTF8Encoding.UTF8; mm.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure; ss.Send(mm); 

Is this a bug?

Answer 2

Stackoverflow said before

In your case it means you have to send it with the email address you logged into Google with.

Stackoverflow also says

So maybe there's a firewall that interferes with the connection. I'm encountering this problem right now while testing your code. Try the suggested TELNET-Test.