SmtpClient with Gmail

Question

I'm developing a mail client for a school project. I have managed to send e-mails using the SmtpClient in C#. This works perfectly with any server but it doesn't work with Gmail. I believe it's because of Google using TLS. I have tried setting EnableSsl to true on the SmtpClient but this doesn't make a difference.

This is the code I am using to create the SmtpClient and send an e-mail.

this.client = new SmtpClient("smtp.gmail.com", 587); this.client.EnableSsl = true; this.client.UseDefaultCredentials = false; this.client.Credentials = new NetworkCredential("username", "password");  try {     // Create instance of message     MailMessage message = new MailMessage();      // Add receiver     message.To.Add("[email protected]");      // Set sender     // In this case the same as the username     message.From = new MailAddress("[email protected]");      // Set subject     message.Subject = "Test";      // Set body of message     message.Body = "En test besked";      // Send the message     this.client.Send(message);      // Clean up     message = null; } catch (Exception e) {     Console.WriteLine("Could not send e-mail. Exception caught: " + e); } 

This is the error I am getting when I try to send an e-mail.

Could not send e-mail. Exception caught: System.Net.Mail.SmtpException: Message could not be sent. ---> System.IO.IOException: The authentication or decryption has failed. ---> System.InvalidOperationException: SSL authentication error: RemoteCertificateNotAvailable, RemoteCertificateChainErrors   at System.Net.Mail.SmtpClient.<callback>m__4 (System.Object sender, System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Security.Cryptography.X509Certificates.X509Chain chain, SslPolicyErrors sslPolicyErrors) [0x00000] in <filename unknown>:0    at System.Net.Security.SslStream+<BeginAuthenticateAsClient>c__AnonStorey7.<>m__A (System.Security.Cryptography.X509Certificates.X509Certificate cert, System.Int32[] certErrors) [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.SslClientStream.OnRemoteCertificateValidation (System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Int32[] errors) [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.SslStreamBase.RaiseRemoteCertificateValidation (System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Int32[] errors) [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.SslClientStream.RaiseServerCertificateValidation (System.Security.Cryptography.X509Certificates.X509Certificate certificate, System.Int32[] certificateErrors) [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.validateCertificates (Mono.Security.X509.X509CertificateCollection certificates) [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.ProcessAsTls1 () [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.Handshake.HandshakeMessage.Process () [0x00000] in <filename unknown>:0    at (wrapper remoting-invoke-with-check) Mono.Security.Protocol.Tls.Handshake.HandshakeMessage:Process ()   at Mono.Security.Protocol.Tls.ClientRecordProtocol.ProcessHandshakeMessage (Mono.Security.Protocol.Tls.TlsStream handMsg) [0x00000] in <filename unknown>:0    at Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0    --- End of inner exception stack trace ---   at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0    --- End of inner exception stack trace ---   at System.Net.Mail.SmtpClient.Send (System.Net.Mail.MailMessage message) [0x00000] in <filename unknown>:0    at P2Mailclient.SMTPClient.send (P2Mailclient.Email email) [0x00089] in /path/to/my/project/SMTPClient.cs:57  

Does anyone have an idea why I might be getting this error?

Answer 1

Gmail's SMTP server requires you to authenticate your request with a valid gmail email/password combination. You do need SSL enabled as well. Without actually being able to see a dump of all your variables being passed in the best guess I can make is that your Credentials are invalid, make sure you're using a valid GMAIL email/password combination.

You might want to read here for a working example.

EDIT: Okay here's something I wrote and tested just then and it worked fine for me:

public static bool SendGmail(string subject, string content, string[] recipients, string from) {     if (recipients == null || recipients.Length == 0)         throw new ArgumentException("recipients");      var gmailClient = new System.Net.Mail.SmtpClient {         Host = "smtp.gmail.com",         Port = 587,         EnableSsl = true,         UseDefaultCredentials = false,         Credentials = new System.Net.NetworkCredential("******", "*****")     };      using (var msg = new System.Net.Mail.MailMessage(from, recipients[0], subject, content)) {         for (int i = 1; i < recipients.Length; i++)             msg.To.Add(recipients[i]);          try {             gmailClient.Send(msg);             return true;         }         catch (Exception) {             // TODO: Handle the exception             return false;         }     } } 

If you need any more info there's a similar SO article here