How can authentication failure mimic reputation loss?

Authentication failure symptoms:

Similar to reputation issues:

Increased spam folder placement

Higher bounce rates

Delivery rejections

Key differences:

Sudden onset (when authentication broke)

Affects all mail equally

Headers show authentication failures

Postmaster tools show auth errors

Diagnosis:

Check email headers for Authentication-Results

Look for spf=fail, dkim=fail, dmarc=fail

Review Postmaster Tools authentication section

Common causes:

DNS changes breaking records

ESP configuration changes

DKIM key rotation issues

SPF record modifications

Expired credentials look like a bad reputation to inspectors. Fix the paperwork first.