Access denied, sending domain does not pass DMARC verification and has a DMARC policy of reject

This is super annoying. I'm not using Microsoft "defender". I'm on the receiving end of its stick.

I noticed that when I start sending emails back and forth with some business that uses Microsoft 365 Defender to handle their emails, it works for a few initial emails. Maybe .about 5. But then all of a sudden my messages start bouncing back with the following message:

"Diagnostic-Code: smtp;550 5.7.509 Access denied, sending domain ____.com does not pass DMARC verification and has a DMARC policy of reject."

I tested my email for passing DMARC and found no issues with multiple services that do those DMARC tests. So the problem is clearly with the "defender".

I also noticed that if I resend the message the next day, it goes through. But only if I don't send too many emails - which is generally about 5.

Does anyone have any idea when will they fix it?