MailFixIt

Generic SMTP delivery response

Understand SMTP 5.7.1: Delivery not authorized

The receiving system permanently refused this sender, message, host, or relay action under an authorization policy.

Problem description

A representative response is:

550 5.7.1 Delivery not authorized.
Is this temporary or permanent?

Do not repeatedly resend the same message. Obtain permission or correct the specific policy or relay configuration first.

What this response means

Standard 5.7.1 Delivery not authorized, message refused is permanent. A receiver may use it for a recipient allowlist, restricted group, transport rule, relay denial, host filter, or another access policy.

Fix it

  1. Preserve the full response, receiver hostname, sender, recipient, connecting IP, and message ID.
  2. If it names a recipient or group restriction, ask the recipient owner or administrator to authorize the sender.
  3. If it says unable to relay, send through the correct authenticated relay or configure the receiving system to accept the intended domain.
  4. If an organization rule rejected the message, ask its administrator which condition matched before changing the message.
  5. If it names IP, content, or reputation filtering, correct that specific cause and send one controlled test.

Do not assume 5.7.1 means SPF, DKIM, or DMARC. Change authentication DNS only when the full response says it failed.

What MailFixIt can check

MailFixIt can inspect public email DNS when relevant. It cannot see recipient permissions, transport rules, relay credentials, or private block lists.

Use a provider-specific page whenever its wording identifies a narrower cause.

Frequently asked questions

What does SMTP 5.7.1: Delivery not authorized mean?

The receiver does not authorize this delivery. The exact response is needed to distinguish recipient restrictions, relay denial, transport rules, and filtering policy.

Can MailFixIt prove this entire bounce from public DNS?

No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.

Related email diagnostics

SMTP 550 5.7.26: Multiple authentication checks failedUnderstand SMTP 5.7.26 and separate SPF, DKIM, DMARC, and alignment failures before changing email DNS.

Primary sources: IANA SMTP Enhanced Status Codes.