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 . . .

I'd recommend taking a look at this question

Brian Driscoll
– Brian Driscoll

2011-04-28 13:07:52 +00:00
Commented Apr 28, 2011 at 13:07 — Brian Driscoll
– Brian Driscoll, Commented Apr 28, 2011 at 13:07

Ferruccio · Accepted Answer · 2011-04-28 13:21:19Z

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); }

Is this still working for you? This is the exact code that I had used in the past, but with Google's recent conversion to their "shared" setup for google apps mail, this appears to have stopped working, getting the error that the OP is getting.
@Charles Boyung: It worked as of April 19, 2011. The system sends me an email with a stack trace whenever there's an unhandled exception. So it's a rare event. I will test it again.
I just tested it. It's still working. Perhaps the problem is in the gmail settings.
Has your google apps domain been converted yet? Wondering if the conversion changes something.
I'm not sure what you mean by "google apps domain". I'm not using google apps, just a gmail account.

Charles Boyung · Accepted Answer · 2011-05-01 22:14:51Z

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>

danyloid · Accepted Answer · 2011-04-28 13:33:19Z

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.

danielonsombi · Accepted Answer · 2021-05-19 19:57:37Z

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

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