How Do I: Enable SSL for PasswordRecovery Email

I received the following error message when using the PasswordRecovery control:

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Must issue a STARTTLS command first b37sm394701ana

 I believe I need to set EnableSsl="true" for the default SmtpClient used by the PasswordRecovery control. However, I couldn't find a simple way to do it. Can someone help out? 
...