how to FIX "550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)"

How do I get Microsoft out of my business and get rid of the above result when I send emails?

I have been coordinating communications among my neighbors for more than 20 years via email. This includes sending them one email each week that contains a newsletter. They have all given me their e-addresses voluntarily, and I always send emails using BCC so I'm not sharing their e-addresses with anyone else. I bet God doesn't even know why for the last 6 weeks, Microsoft REFUSES TO DELIVER my emails to my neighbors! I only get the above message! Even the copies I sent to myself get rejected!! What they heck??? What AI Bot is on control? And how do we disable it? I am NOT buying 365 though that seems to be what Microsoft is forcing on us!