Microsoft SMTP block lists

Background Completely out of the blue I received a similar message when trying to send mail to outlook.com live.com hotmail.com & msn.com host msn-com.olc.protection.outlook.com[52.101.41.123] said: 550 5.7.1 Unfortunately, messages from [97.107.133.211] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BE4A91A461D87F] [BY1PEPF000264AF.namprd02.prod.outlook.com 2026-10-09T23:50:55.394Z 08DF2548D36B9F2E] (in reply to MAIL FROM command) Our servers have been sending mail to these domains for years without any issues and this pops up out of the blue. In full disclosure, yes we do all the SPF,DKIM,DMARC stuff and we are not on any public block lists. Searching around it took a while to find an appropriate course of action. The link they send is close to worthless in trying to resolve the…