SmtpClient.Credentials Property

Some SMTP servers require that the client be authenticated before the server will send e-mail on its behalf. To use your default network credentials, you can set the UseDefaultCredentials to true instead of setting this property. If the UseDefaultCredentials property is set to false, then the value set in the Credentials property will be used for the credentials when connecting to the server. If the UseDefaultCredentials property is set to false and the Credentials property has not been set, then mail is sent to the server anonymously.

Credentials information can also be specified using the application and machine configuration files. For more information, see <mailSettings> Element (Network Settings). If information is specified using the Credentials property, this information overrides the configuration file settings.

Caution
If you provide credentials for basic authentication, they are sent to the server in clear text. This can present a security issue because your credentials can be seen, and then used by others.

The following code example demonstrates setting the credentials used to send an e-mail.

		public static void CreateTestMessage1(string server, int port)
		{
			string to = "jane@contoso.com";
			string from = "ben@contoso.com";
			string subject = "Using the new SMTP client.";
			string body = @"Using this new feature, you can send an e-mail message from an application very easily.";
			MailMessage message = new MailMessage(from, to, subject, body);
			SmtpClient client = new SmtpClient(server, port);
			// Credentials are necessary if the server requires the client 
			// to authenticate before it will send e-mail on the client's behalf.
			client.Credentials = CredentialCache.DefaultNetworkCredentials;

      try {
			  client.Send(message);
      }
			catch (Exception ex) {
			  Console.WriteLine("Exception caught in CreateTestMessage1(): {0}", 
                    ex.ToString() );
      }              
		}

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference