C# – Why I use google ‘smtp’ cannot send out email

cemailgmailsmtp

I have the following program to send an email by using "smtp.gmail.com:587"

namespace TestMailServer
{
    class Program
    {
        static void Main(string[] args)
        {
            MailMessage mail = new MailMessage();
            SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");
            mail.From = new MailAddress("myTest@gmail.com");
            mail.To.Add("myTest2@gmail.com");
            mail.Subject = "Test Mail";
            mail.Body = "This is for testing SMTP mail";

            SmtpServer.Port = 587;
            SmtpServer.Credentials = new System.Net.NetworkCredential("myTest@gmail.com", "myPassword");
            SmtpServer.EnableSsl = true;
            SmtpServer.Send(mail);
            Console.WriteLine("Send out");

        }
    }
}

myTest@gmail.com, myTest2@gmail.com are really existing and myTest@gmail.com's password is myPassword. Why I got the following error:

Unhandled Exception:
System.Net.Mail.SmtpException: 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 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
TestMailServer.Program.Main(String[]
args) in D:\visual studio
2010\Projects\TestMailServer\TestMailServer\Program.cs:line
26 Press any key to continue . . .

Best Answer

I'm not sure what is causing your problem. Here is some code I have been using to successfully send email through a gmail account:

const string from = "...";
var fromAddr = new MailAddress(from, "Bug Tracker");
var toAddr = new MailAddress("...@...", "...");
var client = new SmtpClient {
    Host = "smtp.gmail.com",
    Port = 587,
    EnableSsl = true,
    DeliveryMethod = SmtpDeliveryMethod.Network,
    UseDefaultCredentials = false,
    Timeout = 30 * 1000,
    Credentials = new NetworkCredential(fromAddr.Address, "...")
};
using (var msg = new MailMessage(fromAddr, toAddr)) {
    msg.Subject = "...";
    msg.Body = string.Format("username: {0}\nversion: {1}\n\n{2}", Environment.UserName, Assembly.GetExecutingAssembly().GetName().Version.ToString(3), cbtext);
    client.Send(msg);
}
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