Comcast rejecting legitimate Microsoft 365 sender – 530 5.1.0

A legitimate Microsoft 365 sender is being rejected when sending to multiple Comcast.net recipients with “530 5.1.0 sender rejected.” I contacted Customer Security Assurance and was directed to the online reporting form, but that form requires a sending IP address that is not provided in the Microsoft 365 non-delivery report. I have the complete diagnostic information and would like assistance escalating this to the appropriate email/Postmaster team.