530 5.7.1: client was not authenticated
The receiving server requires authentication before it accepts a message, and the sending system did not authenticate.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 530 5.7.1
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
530 5.7.1 Client was not authenticated
What it means
This 5.7.1 variant comes from a server that only accepts messages from systems that authenticate first. Microsoft's example is 530 5.7.1 Client was not authenticated from a server configured not to accept anonymous email from the internet. The report's diagnostic section names the server that refused. If it belongs to the recipient's organization, its administrators are responsible for the setting; if it is a server you submit mail through, your sending system has to be configured to authenticate.
Common causes
- The receiving server is set to refuse anonymous mail from the internet.
- An application or device submits mail without signing in.
How to fix it
- 01Read the diagnostic section of the report to see which server refused the message.
- 02If it is the recipient's server, tell their admin that it rejects anonymous internet mail.
- 03If it is a server you submit through, configure the sending system to authenticate with valid credentials.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
- 550 5.7.57SMTP client submission without authentication.A device or application tried to send through smtp.office365.com without authenticating as a user with an Exchange Online mailbox.
- 530Authentication required.The server requires the client to log in, or to start TLS, before it accepts this command, which usually means before it accepts any mail.
- 5.7.1Delivery 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.
5.7.1 at other providers
- 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.
- 550 5.7.1IPv6 sender without PTR or authentication.Gmail rejected mail that arrived over IPv6 because the sending address lacks a matching PTR record, or the message failed authentication.
- 550 5.7.1Blocked for low IP reputation.Gmail permanently rejected the message because the IP it came from has a very low reputation with Gmail.
- 550 5.7.1Blocked for low domain reputation.Gmail permanently rejected the message because the domain it comes from has a very low reputation with Gmail.
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