Message Center

You can send private messages to other website members.  This includes '61 and '63 unlisted guest members.  The recipient gets an email notice that a message has been sent.  The recipient has to log in to the website to receive or send a message, so it's completely private.  

Log in and click on Message Center under Member Functions.  Click on Compose Message.  Type in any part of the recipient's name, and the name will pop up.