Assembly: System (in System.dll)
You cannot change the value of this property when an e-mail is being sent.
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 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 property is set to false and the Credentials property has not been set, then mail is sent to the server anonymously.
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.