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?

​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?  Read More

​