Marty,

           The Private button is present on the Groups.io web interface (on groups that allow private messaging) and appears directly below the compose box.  It allows you to send a response only to the individual whose message you're responding to.

           You can get the same effect in the e-mail interface using the "Reply to Sender" link at the bottom of each and every message that gets sent out by Groups.io, presuming you're not using plain text for your message format.
--

Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763  

  If you remove all the homosexuals and homosexual influences from what is generally regarded as American culture, you are pretty much left with Let's Make a Deal.

          ~ Fran Lebowitz