Sending mail via gmail from C# is giving an unexpected errors

Question

I am trying to send an e-mail from my c# WinForms application using g-mail SMTP Server. Here is my code:

        string fromEmail = txtFromEmail.Text.Trim();
        string toEmail = txtToEmail.Text.Trim();
        string[] toArray = toEmail.Split(',');

        MailMessage msg = new MailMessage();
        msg.From = new MailAddress(fromEmail);
        for (int i = 0; i <= toArray.Length - 1; i++)
        {
            msg.To.Add(toArray[i]);
        }
        msg.Subject = "Test E-mail";
        msg.Body = "This is a test";
        msg.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
        msg.HeadersEncoding = Encoding.GetEncoding(1252);
        msg.SubjectEncoding = Encoding.GetEncoding(1252);
        msg.BodyEncoding = Encoding.GetEncoding(1252);

        AlternateView av1 = AlternateView.CreateAlternateViewFromString(msg.Body, null, System.Net.Mime.MediaTypeNames.Text.Html);
        msg.AlternateViews.Add(av1);

        smtp = new SmtpClient();
        smtp.Host = txtSMTPServer.Text.Trim();
        smtp.UseDefaultCredentials = false;

        NetworkCredential cred = new NetworkCredential();

        SecureString ss = new NetworkCredential("", txtSMTPPassword.Text.Trim()).SecurePassword;
        cred.UserName = txtSMTPUsername.Text.Trim();
        cred.SecurePassword = ss;

        smtp.Credentials = cred;
        smtp.EnableSsl = chkEnableSSL.Checked;
        smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
        smtp.Port = Convert.ToInt16(txtSMTPPort.Text.Trim());
        smtp.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);


        smtp.SendAsync(msg, msg);

I am getting the following error message:

'e.Error.InnerException.Message' threw an exception of type 'System.NullReferenceException'
Data: {System.Collections.ListDictionaryInternal}
HResult: -2147467261
HelpLink: null
InnerException: null
Message: "Object reference not set to an instance of an object."
Source: "8a9e67622e334c659c856a023d4b1631"
StackTrace: "   at <>x.<>m0(frmSettings <>4__this, Object sender, AsyncCompletedEventArgs e)"
TargetSite: {System.String <>m0(Ariba.frmSettings, System.Object, System.ComponentModel.AsyncCompletedEventArgs)}

I am able to send e-mail with a non-Gmail SMTP server. What am I missing?

I have since changed my send method to synchronous using smtp.Send(msg), but now I am getting a different error:

{"Unable to read data from the transport connection: net_io_connectionclosed."}
Data: {System.Collections.ListDictionaryInternal}
HResult: -2146232800
HelpLink: null
InnerException: null
Message: "Unable to read data from the transport connection: net_io_connectionclosed."
Source: "System"
StackTrace: "   at System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine)\r\n   at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine)\r\n   at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller)\r\n   at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)\r\n   at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint)\r\n   at System.Net.Mail.SmtpClient.GetConnection()\r\n   at System.Net.Mail.SmtpClient.Send(MailMessage message)"
TargetSite: {Int32 ProcessRead(Byte[], Int32, Int32, Boolean)}

I realize this will probably get tagged as duplicate again, since this was probably asked before, but nothing I have read will solve my problem.

BTW: I have set my Google settings to allow unsecure apps.

Something is `null` that shouldn't be `null`. What line is causing the error? Is this line supposed to be `null`? If not, make sure you change that. — Jaskier, Apr 03 '19 at 17:16
It isn't giving the error until it reaches the SendCompletedCallback event — RickInWestPalmBeach, Apr 03 '19 at 17:18
@RickInWestPalmBeach Shouldn't you be awaiting this: `smtp.SendAsync(msg, msg);` as `await smtp.SendAsync(msg, msg);` — Ryan Wilson, Apr 03 '19 at 17:20
@RyanWilson No, SmtpClient predates the Task based asynchronous pattern. `SendAsync` returns void. However, `SendMailAsync` returns a Task and can be awaited. — mason, Apr 03 '19 at 17:23
The AsyncCompletedEventArgs in my SendCompletedCallback event is not null. — RickInWestPalmBeach, Apr 03 '19 at 17:24
I forgot to mention that the e.Error.Message gives me "Syntax error, command unrecognized. The server response was: " (And nothing else). The error information above was the Inner Exception. — RickInWestPalmBeach, Apr 03 '19 at 17:29
This is not a duplicate. I know what a NullReferenceException is. I am getting the error AFTER I send the e-mail as a response from Google. Apparently Google is receiving a value as null? — RickInWestPalmBeach, Apr 03 '19 at 17:35

Joel Coehoorn · Answer 1 · 2019-04-04T01:20:14.223

0

We see the real error is here:

net_io_connectionclosed

This means GMail reject your connection.

This is expected.
GMail no longer accepts regular authentication for SMTP connections by default!
It hasn't for a few years now.

If you want to use an GMail as a traditional SMTP server, you must do one of three things:

Enable 2-Factor authentiation and set up a Per-App Password

or

Support OAuth authentication

or

Enable Less Secure Apps

If you don't do one of those things, GMail will reject your SMTP connections.

edited Apr 04 '19 at 01:20

answered Apr 04 '19 at 01:18

Joel Coehoorn

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As stated above, I already enabled "Less Secure Apps", and I am still getting the same error. – RickInWestPalmBeach Apr 04 '19 at 01:19

Sending mail via gmail from C# is giving an unexpected errors

1 Answers1