c# SmtpClient class not able to send email using gmail

问题

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("donotreply@domain.com", "destination@domain.com", "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()

回答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("donotreply@domain.com", "destination@domain.com", "subject here", "my body");
mm.BodyEncoding = UTF8Encoding.UTF8;
mm.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
ss.Send(mm);

Is this a bug?

回答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.

回答3:

Work for me only with port 25.

回答4:

This works, but it's not very performance friendly. Check out client.SendAsync: http://msdn.microsoft.com/en-us/library/x5x13z6h.aspx

An example use case:

 var message = new MailMessage("from", "to", "subject", "body");
 var client = new SmtpClient("smtp.gmail.com", 587)
            {
                Credentials = new NetworkCredential("login", "password"),
                EnableSsl = true
            };
            client.SendCompleted += (s, e) =>
            {
                client.Dispose();
                message.Dispose();
            };
            client.SendAsync(message, null);

回答5:

This work's perfectly. Create a mail Template in a separate file MailTemplate.html.

Add genuine NetworkCredentials - login and Password

private void SendMail()
    {
    string filename = Server.MapPath("~/MailTemplate.html");
    string username = UserName.Text.ToString();

    string mailbody = System.IO.File.ReadAllText(filename);
    mailbody = mailbody.Replace("##NAME##", username);
    string to = Email.Text;
    string from = "test@gmail.com";

    MailMessage message = new MailMessage(from, to);
    message.Subject = "Auto Response Email";
    message.Body = mailbody;
    message.BodyEncoding = Encoding.UTF8;
    message.IsBodyHtml = true;
    SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
    System.Net.NetworkCredential basicCredential = new System.Net.NetworkCredential("test@gmail.com", "test123#");
    client.EnableSsl = true;
    client.UseDefaultCredentials = true;
    client.Credentials = basicCredential;
    try
    {
        client.Send(message);
        SuccessMessage.Text = "Email Sending successfully";

    }
    catch (Exception ex)
    {

        ErrorMessage.Text = ex.Message.ToString();
    }
}

MailTemplate.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <title>Title</title>
</head>
<body>
    <div style="border: thin solid #0066FF; width: 550px; margin: 25px auto; padding: 15px; font-family: 'Microsoft Himalaya'; font-size: x-large; font-style: normal; color: #0066FF; background-color: #EfEFF2;">
        <br />
        <p style="vertical-align: middle">Dear ##NAME##,</p>
    </div>
</body>
</html>

回答6:

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

回答7:

It works fine in my case:

private void btnTestConnection_Click(object sender, EventArgs e)
     {
    btnTestConnection.Enabled = false;
    SmtpClient ss = new SmtpClient(txtSmtpHostName.Text.Trim(), Convert.ToInt32(numSmtpHostPort.Value));
    ss.EnableSsl = chkSmtpSecureType.Checked;
    ss.Timeout = 10000;
    ss.DeliveryMethod = SmtpDeliveryMethod.Network;
    ss.UseDefaultCredentials = false;
    ss.Credentials = new NetworkCredential(txtSmtpAccount.Text.Trim(), txtSmtpPassword.Text);

    MailMessage mm = new MailMessage(txtSmtpFromEmail.Text.Trim(), "test@domain.com", "subject", "my body");
    mm.BodyEncoding = UTF8Encoding.UTF8;
    mm.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
    ss.SendCompleted += (s, b) =>
    {
        ss.Dispose();
        mm.Dispose();
    };
    try
    {
        ss.Send(mm);
        ss.Dispose();
        mm.Dispose();
        MessageBox.Show("Connection successfully");
    }
    catch (Exception ep)
    {
        MessageBox.Show("Connection error: " + ep.Message, "Smtp Connection Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
    btnTestConnection.Enabled = true;
}

来源：https://stackoverflow.com/questions/1311749/c-sharp-smtpclient-class-not-able-to-send-email-using-gmail

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smtpclient