The default behavior for "Reply" for any Groups.io message is "Reply to List" unless a group owner has engineered something very odd, which I have yet to see a single one do.

I will repeat, one last time, if you wish to reply to the sender of a given message, privately, then use the Reply to Sender link at the bottom of that message.  Activating same should trigger your email client or webmail to open a blank message with the sender's address filled in and with the subject reading, "Private:," followed by the title of the actual topic.  Of course, you can alter the Subject to your liking if you so choose.

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Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041  

Always remember that computers are just glorified light bulbs - they rarely fail in continuous use and usually go pop when turned off and on.

        ~ Technician with the username Computer Bloke, on Technibble.com