How can SPF/DKIM misconfigurations cause indirect bounces?

Authentication misconfigurations cause indirect delivery failures:

SPF misconfiguration impacts:

Sending IP not in SPF record. SPF check fails. If DMARC policy is "reject," message bounces. Even "quarantine" may become rejection.

DKIM misconfiguration impacts:

Key mismatch or missing public key. Signature verification fails. DMARC alignment fails. Rejection per policy.

Why "indirect":

Address is valid. Content is fine. Authentication configuration causes rejection. Fix is on sender side, not recipient.

Bounce appearance:

550 5.7.x codes. References to SPF, DKIM, or DMARC in message. "Authentication failed" language.

Resolution:

Audit SPF record for all sending IPs. Verify DKIM key publication and signing. Test with authentication validators.

Authentication errors masquerade as reputation or policy issues. Check configuration before assuming blocklisting.