DMARC: dmarc=fail (p=reject) in Authentication-Results
SPF or DKIM passed on its own but neither aligned with the domain in the From header, and alignment is what DMARC checks. This is why mail sent through a third party can pass SPF against the provider domain and still be rejected as your domain.
Quick fix
Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.
# Read the published policy and the alignment modes (aspf, adkim)
dig +short TXT _dmarc.example.com
# Check alignment on a real message: the From domain must match one of these
# SPF: the envelope sender domain (Return-Path), not the From header
# DKIM: the d= tag of a signature that verified
swaks --to [email protected] --from [email protected] --server smtp.provider.net
# Third party senders need a signing domain you control, set up in their console
dig +short TXT selector1._domainkey.example.com
# Roll out in stages and read the aggregate reports before enforcing
# _dmarc.example.com TXT
"v=DMARC1; p=none; rua=mailto:[email protected]; adkim=s; aspf=r"
"v=DMARC1; p=quarantine; pct=25; rua=mailto:[email protected]"
# Forwarded mail breaks SPF by design, so DKIM alignment is what keeps it deliverableHow to diagnose Email errors
SMTP errors follow a strict convention: a 4xx code is temporary and will be retried, a 5xx is permanent and will not. Beyond delivery mechanics, most modern email problems are authentication problems (SPF, DKIM and DMARC alignment) which cause silent filtering into spam rather than an explicit bounce, and therefore need to be checked proactively.
If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.
- Read the full bounce message. The enhanced status code (for example
5.7.1) is far more specific than the three-digit code and usually names the exact policy that rejected the message. - Test the SMTP conversation manually with
swaks --to [email protected] --server smtp.example.com --tls. It shows each command and response. - Verify SPF, DKIM and DMARC records with
dig TXT example.com,dig TXT selector._domainkey.example.comanddig TXT _dmarc.example.com. - Check DMARC alignment, not just presence: the domain in the
From:header must align with the SPF or DKIM domain, or DMARC fails even when both pass individually. - Confirm the sending IP is not on a blocklist and has valid reverse DNS. Missing PTR records cause rejection by many large providers.
Tools worth reaching for
swaksdig TXTopenssl s_client -starttls smtppostfix mail logsDMARC aggregate reports
Authoritative references
Primary documentation for this error, worth reading before applying any fix in production.
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Something missing or wrong?
This entry is maintained by hand. If the fix is out of date, incomplete, or you have a better one, email a correction and it will be reviewed.