"554 5.7.9 Message not accepted for policy reasons" delivery error

If you receive a "554 5.7.9 Message not accepted for policy reasons" delivery error, it may be due to an issue with the sender not using DMARC.

When an email is automatically forwarded from one provider to another, it may appear to come from an unauthorized server if the provider isn't using DMARC.

To check if your email was sent using DMARC, you'll need to view the raw message.

Once you have the raw message data, look for the following keywords:

• X-Yahoo-Forwarded - means it was forwarded and the line should include the address to which it was forwarded.
• p=reject - means the original domain is using DMARC and per their instructions, the email is being rejected.