c# SmtpClient class not able to send email using gmail

Question

Hi,

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

The same settings work fine in Thunderbird.

Heres 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

In order to prevent spamming, it is necessary that you authenticate when you want to sent mail accross domains.

you can simply do this:

SmptClient client = new SmtpClient();
...
SmtpClient.Credentials = CredentialCache.DefaultNetworkCredentials

and it should work.

Answer 2

Stackoverflow said before

In your case it means u have to send with the email adress you logged into google with.

Stackoverflow also says

So maybe theres a firewall that interferes the connection. Im encountering this problem right now while testing your code. Try the suggested TELNET-Test.

Answer 3

This is silly, you won't belive what fixed my problem.

This line,

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

must be declared AFTER

ss.UseDefaultCredentials = false;

So the final working code 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 4

I can verify that setting UseDefaultCredentials to false MUST be done before the NetworkCredentials is created. I had the same problem.

Answer 5

Impossible. I tried everything. It is not possible to use a googlemail account for automaticall sending emails. One day it works, the other day the email is refused. I surrender..