Why I use google 'smtp' cannot send out email?

Question

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("[email protected]");
            mail.To.Add("[email protected]");
            mail.Subject = "Test Mail";
            mail.Body = "This is for testing SMTP mail";

            SmtpServer.Port = 587;
            SmtpServer.Credentials = new System.Net.NetworkCredential("[email protected]", "myPassword");
            SmtpServer.EnableSsl = true;
            SmtpServer.Send(mail);
            Console.WriteLine("Send out");

        }
    }
}

[email protected], [email protected] are really existing and [email protected]'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 . . .

Answer 1

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);
}

Answer 2

I had the code that Ferruccio posted and this recently stopped working. I moved my settings into the .config file for my site and it started to work again:

<system.net>
    <mailSettings>
        <smtp from="fromEmail" deliveryMethod="Network">
            <network defaultCredentials="false" enableSsl="true" host="smtp.gmail.com" port="587"
                 userName="fromEmail" password="password"/>
        </smtp>
    </mailSettings>
</system.net>

Answer 3

As far as i remember by default UseDefaultCredentialsProperty is set to true. So that could cause the authentification error you've got. try to add these lines from the previous answer to your code

SmtpServer.DeliveryMethod = SmtpDeliveryMethod.Network;
SmtpServer.UseDefaultCredentials = false;

I've experienced couple of weird exceptions if not set DeliveryMethod property explicitly.

Answer 4

Been struggling with the same error. With smtp.gmail.com, google blocks any attempts to login in to the sender email unless it be authenticated. Login to your email account and act on the sent verification mail. This will grant access to your C# Application