5.7.1: delivery not authorised
The receiving server refuses the message because this sender is not allowed to send to this recipient, as a result of filtering by host or by recipient.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.7.1
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
5.7.1 Delivery not authorized, message refused
What it means
5.7.1 is the most common policy rejection. RFC 3463 defines it as the sender not being authorised to send to the destination, as a result of per-host or per-recipient filtering, and calls it useful only as a permanent error. In practice it covers a wide range: relaying refused, a sending IP on a blocklist, a failed SPF check (RFC 7208 shows 550 5.7.1 for an SPF fail, before RFC 7372 added 5.7.23), a recipient who accepts mail only from certain senders, or a provider's own filter. A 4.7.1 form means the refusal is temporary, for example a rate limit, and the sending server retries. The text after the code matters most here.
Common causes
- Your sending IP or domain is on a blocklist the receiver uses.
- SPF, DKIM or DMARC checks failed and the receiver's policy rejects such mail.
- You tried to relay through a server that does not relay for you, for example by sending without logging in.
- The recipient's domain accepts mail only from certain senders or through its own gateway.
- A provider's spam or reputation filter refused the message.
How to fix it
- 01Read the reply text: it usually names the reason (blocklist, SPF, relay, policy) and may link to a help page.
- 02Check your sending IP and domain on blocklists, and request removal once the cause is fixed.
- 03Check SPF, DKIM and DMARC for the sending domain.
- 04If the text mentions relaying, make sure your client logs in to your own outgoing server.
- 05If only one recipient's domain refuses you, contact its administrator with the full bounce.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
- 554Transaction failed.The server permanently refused the transaction, often after receiving the message data or straight away when the connection opened.
- 550 5.7.23SPF check failed.The SPF check on the sending server's IP address gave a fail result for the sender's domain, and the receiving server's policy rejects such mail.
- 550 5.7.26Multiple authentication checks failed.The message failed more than one authentication check, for example SPF and DKIM, and the receiving server's policy rejects it.
- 5.7.0Security or policy refusal, unspecified.The message or session was refused for a security or policy reason that the server did not describe more precisely, or chose not to reveal.
5.7.1 at other providers
- 5.7.1Unable to relay.The receiving system refused to pass the message on because it is not the final destination for the recipient domain.
- 5.7.1IP listed on both a connector and the IP Allow list.An outside server's IP is set on both an inbound connector and the IP Allow list, which hides the real blocklist that refused it.
- 5.7.1Sending IP on the Microsoft 365 blocklist.Microsoft 365 refused the message because the sending IP address is on its own blocklist, named Blocklist 1 in the bounce.
- 550 5.7.1Blocked by a domain policy.A rule set by the recipient's or the sender's Google Workspace admin blocks this message, so Gmail rejected it under that policy.
- 550 5.7.1Relay IP does not match the sending domain.Google's SMTP relay knows your IP, but the mail's sending domain is not one that IP is registered to relay for in your Workspace account.
- 550 5.7.1Blocked as likely spam.Gmail's filters judged this message likely to be spam and rejected it outright, instead of delivering it to the spam folder.
Further reading
All 105 standard codesEvery code in the wikiPaste your own bounce