Permanent (5xx)
554 5.7.9
Message not accepted for policy reasons (authentication failure)
The message failed an authentication check the receiving server enforces, most often DMARC.
Common causes
- DMARC record set to p=reject and the message failed SPF and DKIM alignment.
- Sending through a relay that breaks SPF/DKIM alignment.
What to do
- →Confirm the `From` domain's SPF and DKIM both align with the actual sending domain, not just a subdomain or forwarding relay.
- →Test with a DMARC checker before setting your own policy to p=reject.