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
Marketer view

Email marketer from Reddit User /r/emailadmin shares that the error often occurs when your email server tries to send mail through another server that isn't configured to allow relaying from your server. Ensure your SMTP authentication is correctly configured and that your server's IP address is whitelisted, if required.

November 2022 - Reddit
Marketer view

Email marketer from Super User Community shares that a common configuration mistake leading to the 'Relaying Denied' error is the absence of proper SMTP authentication. Always ensure that your mail client or application is authenticating with the mail server using valid credentials.

December 2021 - Super User
Marketer view

Email marketer from Stack Overflow User explains that to diagnose a 'Relaying Denied' error, check your mail server's configuration to ensure you are properly authenticated and authorized to send emails. Also, verify your MX records and ensure that your sending server is permitted to relay mail through the destination server. Tools like `nslookup` or `dig` can help verify DNS settings.

January 2022 - Stack Overflow
Marketer view

Email marketer from MXToolbox answers that common causes include incorrect SMTP settings, lack of authentication, or the server being blocked by the recipient's mail server. Ensure your sending server has proper SPF and DKIM records to verify its legitimacy.

November 2023 - MXToolbox
Marketer view

Email marketer from SparkPost answers that a 'Relaying Denied' error, often accompanied by messages like '550 5.7.1', means the server you're trying to send mail through isn't authorized to relay mail from your domain to the recipient's domain. This typically happens because the server requires authentication or because your domain isn't properly configured for sending.

April 2021 - SparkPost
Marketer view

Email marketer from DigitalOcean Community answers that, if you're running a mail server on a DigitalOcean droplet, the 'Relaying Denied' error might occur if the server isn't configured to allow relaying from outside networks. Configure your mail server to authenticate incoming connections and authorize relaying for specific IP ranges or authenticated users.

October 2021 - DigitalOcean
Marketer view

Email marketer from SiteGround answers that it is an error message that indicates the mail server you are using is not allowed to send emails to the specified recipient. This can happen if you're trying to send email through a server that is not configured to relay mail for your domain or if the receiving server has rejected your email.

August 2023 - SiteGround

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.

September 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
Expert view

Expert from Email Geeks explains the 'relaying denied' error usually means the destination domain is dead, has broken its DNS, or is having serious problems with a service migration.

October 2024 - Email Geeks
Expert view

Expert from Email Geeks shares that doing a manual lookup of the MX, then checking delivery to each of the MXes using swaks with a —quit-after TO will probably give you the details you need to explain it.

December 2022 - 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
Technical article

Documentation from Exim Wiki explains that the 'Relaying Denied' error typically arises when the sending mail server is not permitted to forward mail through the recipient's server. This usually occurs because the sending server is not authenticated or is not recognized as a trusted relay.

June 2023 - Exim Wiki
Technical article

Documentation from cPanel explains that a 'Relaying Denied' error occurs when the mail server you're using isn't authorized to send mail on behalf of the domain you're using. This can be due to incorrect MX records, authentication issues, or the server being configured to prevent unauthorized relaying.

February 2022 - cPanel
Technical article

Documentation from Sendmail.org describes the relaying controls in Sendmail, explaining that the server must be configured to explicitly allow relaying from a given source to a given destination. This can be controlled through access databases or other configuration mechanisms.

April 2024 - Sendmail.org