Outlook 2016 How tell Outlook not to trust sender?


Outlook version
Outlook 2016 64 bit
Email Account
Office 365 Exchange
When I mark a message Not Junk, Outlook for O365
asks me whether always to trust messages from that sender, and the check box starts as checked. I can either click OK or uncheck the box then click OK. How do I set OL so that the box is UNchecked by default? I don't see anything related under Options, but maybe there's a Registry key or some other trick... Thank you.