smtp bounce code
550 5.7.26Unauthenticated email is not accepted
what to do
Keep the address, fix your side
Your SPF, DKIM or DMARC failed. The recipient is fine. This is a problem with your sending domain and it will affect every message you send.
What the server is telling you
Since Google and Yahoo tightened bulk sender requirements, mail that fails authentication from a domain sending at volume is rejected outright rather than filed as spam.
Next steps
- →Do not suppress anything. Fix your own DNS.
- →Publish SPF, DKIM and DMARC and make sure they align with your From domain.
- →Check what your domain publishes right now with a free audit.
Commonly returned by: Gmail, Yahoo
Find these before you send, not after
Paste a list and see which addresses sit on domains that accept no mail, which are one character from a real inbox, and which are on catch-all domains where nothing can tell you anything. Free, no signup, nothing stored.
Check a list →