554 5.7.9 Message Not Accepted for Policy Reasons (Yahoo / AOL)

What’s actually happening

Mail to yahoo.com, aol.com, or other Yahoo-run domains bounces with 554 5.7.9 and a link to postmaster.yahooinc.com. This is a hard rejection: the message failed Yahoo's sender requirements and won't be retried. Since Yahoo and Google tightened bulk-sender rules in February 2024, missing or misaligned authentication is the usual trigger. The bounce text often points at the specific error code to look up.

Common causes

• DMARC failure — the From domain has a p=reject or p=quarantine policy and the message didn't align with SPF or DKIM
• Missing DKIM signature, so the message can't establish DKIM alignment with the From domain
• SPF fail or no SPF record for the sending domain
• Poor IP/domain reputation from spam complaints, spam-trap hits, or sudden volume spikes
• Bulk sending (5,000+/day to Yahoo) without a working one-click unsubscribe (List-Unsubscribe header), now a hard requirement

How to fix it

1. Look up the exact error codeThe bounce references a numbered code at postmaster.yahooinc.com/error-codes. That page distinguishes auth failures from reputation or content blocks — fix the one Yahoo actually cited, not a guess.
2. Pass DMARC with aligned SPF and DKIMPublish SPF and DKIM, and make sure at least one aligns with the visible From domain. Add a DMARC record (start at p=none with rua= reporting, then tighten). Misalignment is the most common 5.7.9 cause post-2024.
3. Add one-click unsubscribeFor bulk mail, include List-Unsubscribe and List-Unsubscribe-Post headers so one-click unsubscribe works. Yahoo and Gmail require it for high-volume senders and reject without it.
4. Repair sending reputationKeep your spam complaint rate under 0.3% (target ~0.1%). Purge unengaged and bounced addresses, stop buying lists, and warm up new IPs gradually instead of blasting volume.
5. Enroll in Yahoo's sender toolsRegister at the Yahoo Sender Hub / Complaint Feedback Loop (CFL) to see complaint data and request review. Use it to confirm the fix landed before resuming full volume.