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Yahoo 550 5.7.9: sender is unauthenticated

550 5.7.9Blocked because the sender is unauthenticatedPermanent: retrying will not helpFrom Yahoo Mail and AOL

Typical wording
550 5.7.9 This mail has been blocked because the sender is unauthenticated. Yahoo requires all senders to authenticate with either SPF or DKIM.

What it means

Yahoo announced sender requirements together with Google in 2024. Every sender, regardless of volume, must authenticate with SPF or DKIM; bulk senders also need DMARC, alignment, and one-click unsubscribe. This bounce, which usually reads like the example, means Yahoo saw no passing SPF or DKIM for the message and refused it permanently.

It is different from 554 5.7.9, which is a content or policy rejection of a message that may well be authenticated. It is closer to Gmail’s 5.7.26: the fix is entirely in DNS and in how your server signs mail.

Likely causes

  • The envelope sender domain has no SPF record, or the record leaves out the IP that sent the mail.
  • No DKIM signature on the message, or a signature whose key cannot be found in DNS.
  • A web server or application sending directly with a From address on a domain it is not authorised for.
  • SPF returns permerror because of too many DNS lookups or two SPF records.

How to fix it

  1. Find the IP that connected to Yahoo in your MTA log and test it against the SPF record for your Return-Path domain.
  2. Add the missing sender, for example `v=spf1 ip4:203.0.113.90 include:spf.example.net -all`, keeping a single record under 10 lookups.
  3. Enable DKIM signing on the sending system and publish the selector record it provides.
  4. Publish DMARC if you send in volume, starting with `v=DMARC1; p=none; rua=mailto:dmarc@example.com`.
  5. Send a test to a Yahoo address and inspect the Authentication-Results header for spf=pass or dkim=pass.

Checks that apply

  • SPF Check Tests whether your SPF record permits the IP Yahoo saw, and counts lookups.
  • DKIM Check Confirms the public key for your selector resolves and parses.
  • Google/Yahoo Compliance Checks the requirements Gmail and Yahoo share, so both receivers accept your mail.
See the example diagnosed

The classification runs without network lookups and we never store your paste.

FAQ

Do I need both SPF and DKIM for Yahoo?
One passing mechanism avoids this specific block. Bulk senders should have both plus a DMARC record.
Does this affect AOL addresses too?
Yes, in practice. AOL Mail runs on Yahoo’s mail platform and applies the same sender requirements.

Yahoo Sender Hub

All 191 bounce codes