It's because the mailing list sends as "From: original sender address". Boost's mail server is not an allowed sender of "@Microsoft.com" mail so this gets triggered.
Billy3
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From: Boost
Why is this message in Spam? It has a from address in microsoft.com but has failed microsoft.com's required tests for authentication. Learn more
I think this list isn't configured properly.. and this causes some messages to end up in Spam consistently.. Who's responsible for the mailing list infrastructure? Gr, -- Olaf _______________________________________________ Unsubscribe & other changes: https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.boost.org%2Fmailman%2Flistinfo.cgi%2Fboost&data=01%7C01%7Cbion%40microsoft.com%7Cb9f6c7987cd545ea14ba08d3ef4e0d74%7C72f988bf86f141af91ab2d7cd011db47%7C1&sdata=CI%2BgPdpfLVmfcqp20JiZol7H7rcTEFZHxGpWIBL5jCc%3D&reserved=0