SMTP : error relaying

Question

i am creating an email client that sends e-mail address from server ip instead of SMTP , i wrote that code:

SmtpClient server = new SmtpClient("50.23.128.66");
MailMessage msg = new MailMessage("from@yahoo.com", "tome@yahoo.com", "subject", "body");
server.Send(msg);

but when i run it , i get that error:

Unhandled Exception: System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: 5.7.1 Relaying Denied. at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressColl ection recipients, String deliveryNotify, SmtpFailedRecipientException& exception)

* By the way i am using Windows Server 2008 * and i configured the smtp server to localhost and port 25 , but i don`t know what is that relying error .

Answer 1

Relaying is the method the SMTP server uses to authenticate that it should route the email from a particular sender. An "open relay" means that there is no authentication and the SMTP server will send email sent from anyone. This is not a good practice and there are probably some mechanisms on this particular SMTP server to authenticates, such as a user name and password or even the IP address of the sender. Check with the administrator of the SMTP server to see what is required. I would think at a minimum you would need to set the user name and password, which you did not do in your code example.

Answer 2

If you are using you localhost to rely email, you should be using 127.0.0.1 or localhost instead of that ip address you posted in your code.