In a notable development that will affect numerous businesses globally, Microsoft has announced that it will commence the rejection of emails that do not adhere to strict authentication standards, resulting in the error code "550 5.7.15 Access denied."
This isn’t Microsoft’s announcement. They announced over a month ago. This also only affects bulk senders sending over 5,000 emails a day inbound to their Hotmail/Outlook.com service.
And if you can’t send DMARC-compliant emails in 2025, frankly you deserve to be blocked.