SmtpClient.UseDefaultCredentials Property

Some SMTP servers require that the client be authenticated before the server sends e-mail on its behalf. Set this property to true when this SmtpClient object should, if requested by the server, authenticate using the default credentials of the currently logged on user. For client applications, this is the desired behavior in most scenarios.

Credentials information can also be specified using the application and machine configuration files. For more information, see <mailSettings> Element (Network Settings).

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.

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 using this property.

		public static void CreateTestMessage2(string server)
		{
			string to = "jane@contoso.com";
			string from = "ben@contoso.com";
			MailMessage message = new MailMessage(from, to);
			message.Subject = "Using the new SMTP client.";
			message.Body = @"Using this new feature, you can send an e-mail message from an application very easily.";
			SmtpClient client = new SmtpClient(server);
			// Credentials are necessary if the server requires the client 
			// to authenticate before it will send e-mail on the client's behalf.
			client.UseDefaultCredentials = true;

      try {
			  client.Send(message);
			}  
			catch (Exception ex) {
			  Console.WriteLine("Exception caught in CreateTestMessage2(): {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