What causes a 'relaying denied' error when sending emails, and how can I diagnose the issue?

Summary

The 'Relaying Denied' error arises when a mail server lacks authorization to send emails on behalf of a domain, often due to misconfigurations, authentication issues, or restrictive relay policies. These problems can include a failing destination domain, broken DNS, incorrect MX records, or the server being configured to prevent unauthorized relaying. To diagnose, verify MX records, ensure proper authentication (SMTP, SPF, DKIM), confirm the sending server's IP is whitelisted if necessary, and manually test delivery. Proper configuration, authentication, and explicit permission for relaying are key to resolving the error.

Key findings

  • Authorization Failure: Mail server lacks authorization to send emails on behalf of the domain.
  • Misconfigurations: Incorrect SMTP settings, MX records, or relay configurations contribute to the error.
  • Authentication Issues: Lack of proper SMTP authentication or recognition as a trusted relay triggers the error.
  • Restrictive Policies: Anti-relay policies and server configurations prevent unauthorized relaying.
  • Domain Issues: Destination domain may be dead, have broken DNS, or be undergoing service migration.

Key considerations

  • MX Record Verification: Verify and correct MX records to point to the appropriate mail servers.
  • Authentication Implementation: Ensure proper SMTP authentication and recognize trusted relays.
  • Relay Configuration: Configure the mail server to allow relaying from specific IP addresses or networks.
  • Security Policies: Review and adjust anti-relay policies to permit legitimate relaying.
  • Delivery Testing: Manually test delivery to identify failure points using tools like swaks.
  • Whitelist Management: Ensure the server's IP address is whitelisted on receiving servers if required.

What email marketers say
9Marketer opinions

The 'Relaying Denied' error typically indicates that the mail server you're using is not authorized to send emails on behalf of your domain to the recipient's domain. Common causes include incorrect SMTP settings, lack of proper authentication, the server being blocked by the recipient's mail server, or the server not being configured to relay emails for external domains. Diagnosing the issue involves checking mail server configurations, verifying MX records, ensuring proper authentication (SMTP, SPF, DKIM), and confirming that the sending server's IP address is whitelisted if required. Misconfigurations or security measures to prevent spam often trigger this error.

Key opinions

  • Authorization Issue: The mail server isn't authorized to send emails for the specific recipient or domain.
  • Authentication Problems: Lack of proper SMTP authentication is a common cause.
  • Configuration Errors: Incorrect SMTP settings or server configurations can trigger the error.
  • Relay Restrictions: The server is not configured to relay emails for external domains.
  • Recipient Block: The recipient's mail server is blocking the sending server.

Key considerations

  • SMTP Configuration: Verify and correct your SMTP settings to ensure they are accurate.
  • Authentication: Implement and ensure proper SMTP authentication using valid credentials.
  • MX Records: Check your MX records to confirm they are correctly configured and pointing to the right mail servers.
  • SPF/DKIM Records: Ensure your sending server has valid SPF and DKIM records to verify its legitimacy and prevent it from being flagged as spam.
  • IP Whitelisting: If required, ensure your server's IP address is whitelisted on the receiving server.
Marketer view

Email marketer from Namecheap Support shares that the 'Relaying Denied' error means the mail server you are attempting to use is not authorized to send emails for the specific recipient or domain. This can happen if the server is not properly configured to relay emails for external domains, often due to security measures to prevent spam.

August 2022 - Namecheap
Marketer view

Email marketer from LinuxQuestions.org Forum answers that ensure your server's IP address is whitelisted on the receiving server or that you are properly authenticating. The receiving server may be configured to only accept mail from known, trusted sources or authenticated senders.

July 2023 - LinuxQuestions.org

What the experts say
4Expert opinions

The 'Relaying Denied' error commonly arises when a mail server attempts to send email on behalf of a domain without proper authorization. This can be due to issues with the destination domain, such as a dead domain, broken DNS, or service migration problems. It may also occur if the receiving server doesn't recognize itself as the final destination for the email and incorrectly assumes the sender is attempting to use it as a smarthost for relaying. Diagnosing the problem involves manually inspecting MX records and testing delivery to each MX server, verifying proper authentication, and confirming the server is configured to relay email for the domain.

Key opinions

  • Domain Issues: Destination domain may be dead, have broken DNS, or be undergoing service migration.
  • MX Record Misinterpretation: The receiving server doesn't recognize itself as the final destination.
  • Authorization Failure: The sending mail server is not authorized to send email on behalf of the domain.

Key considerations

  • MX Record Verification: Manually look up the MX records to verify their correctness.
  • Delivery Testing: Test delivery to each MX server to identify the point of failure, using tools like swaks.
  • Authentication Check: Ensure the sending server is properly authenticated to relay email.
  • Relay Configuration: Verify that the mail server is configured to relay email for the domain correctly.
Expert view

Expert from Spam Resource explains that 'Relaying Denied' occurs when a mail server is not authorized to send email on behalf of a domain. This can happen because the server is not configured to relay email for the domain, or because the sending server is not properly authenticated.

August 2024 - Spam Resource
Expert view

Expert from Email Geeks explains that the MX record is pointing at a server, so you send mail there. The server doesn't believe it’s a final destination, so thinks you’re trying to use it as a smarthost.

June 2021 - Email Geeks

What the documentation says
5Technical articles

The 'Relaying Denied' error stems from a lack of authorization for the sending mail server to relay emails on behalf of a domain. Documentation across various platforms (cPanel, Exim, Microsoft Exchange, Postfix, Sendmail) highlights that this issue arises due to factors such as incorrect MX records, authentication failures, misconfigured relay settings, or restrictive anti-relay policies. Resolving this typically involves ensuring proper authentication, configuring relay settings to allow specific IP addresses or networks, and verifying that the server is explicitly permitted to relay mail to the intended destination.

Key findings

  • Authorization Failure: The sending mail server is not authorized to relay emails on behalf of the domain.
  • Authentication Issues: The sending server is not properly authenticated or recognized as a trusted relay.
  • Configuration Problems: Incorrect MX records or misconfigured relay settings contribute to the error.
  • Anti-Relay Policies: Default anti-relay policies reject attempts to send mail to external domains unless authenticated or from trusted networks.

Key considerations

  • MX Record Verification: Ensure MX records are correctly configured to point to the appropriate mail servers.
  • Authentication Implementation: Implement and enforce proper authentication mechanisms for sending servers.
  • Relay Configuration: Configure relay settings to allow specific IP addresses, networks, or authenticated users to relay mail.
  • Policy Adjustments: Review and adjust anti-relay policies to permit legitimate relaying while preventing spam and unauthorized use.
Technical article

Documentation from Postfix explains that their default anti-relay policy rejects attempts to send mail to external domains unless the client is authenticated or comes from a trusted network. This policy helps prevent spam and unauthorized mail relaying.

February 2024 - Postfix
Technical article

Documentation from Microsoft Support explains that in Exchange Server, 'Relaying Denied' indicates the server isn't configured to allow relaying from the source IP. To resolve this, you need to configure a receive connector that allows relaying from the specific IP address or network range. Ensure proper authentication is enabled.

August 2021 - Microsoft