SMTP 5.7.1: delivery not authorized, message refused

RFC 3463policy_blockaction: review

5.7.1 is a policy rejection. The receiving server understood the message and refused it on purpose. The cause sits in the accompanying text, which is where the actual diagnosis lives: reputation, content, relaying, or authentication.

What it looks like in the log

550 5.7.1 Relay access denied

550 5.7.1 Service unavailable; Client host [x.x.x.x] blocked using Spamhaus

550 5.7.1 Message rejected due to content restrictions

Why it happens

• The receiver considers you unauthorised to relay through it.
• A blocklist listing named in the response text.
• Content or a URL in the message triggering a filter.
• A recipient-side rule that has nothing to do with your reputation.

What to do

• Read the text after the code. 5.7.1 on its own is not a diagnosis.
• If a blocklist is named, work that listing specifically.
• If it says relay access denied and you are the sender, check that you are connecting to the right host and authenticating.

Related

5.7.26 · 5.7.606 · spamhaus

Classified as policy_block, action review. Paste a response into the bounce classifier to check one against the same ruleset.

Written and maintained by Rastu Singh, an infrastructure engineer working on high-volume email in Tallinn.