Summary
The '550 relaying denied' bounce error arises from a multitude of factors related to authorization, configuration, and reputation. Root causes include the MX server not handling mail for the recipient, DNS and MTA misconfigurations, problems with the receiving email provider, authentication failures, recipient domain policies, reverse DNS mismatches, blacklisting, incorrect HELO/EHLO configurations, improper Google Workspace and Microsoft 365 settings, and incorrect Postfix configurations. Solutions involve ensuring proper SMTP authentication, using valid reverse DNS records, utilizing SMTP relay services, avoiding blacklists, validating the 'From:' address, properly configuring hostnames, employing the correct authentication methods (e.g., TLS), scrutinizing error codes and logs, verifying MX records, checking DNS settings, and carefully reviewing platform specific configurations.
Key findings
- Authorization & Authentication: Lack of authorization to send on behalf of the domain and improper SMTP authentication are leading causes.
- DNS & MTA Configuration: DNS caching issues, incorrect MTA configurations, and reverse DNS mismatches contribute to the error.
- Provider-Side Issues: Problems originating from the recipient's email provider (e.g., Yahoo) can trigger the error.
- Domain Policies & Reputation: Recipient domain policies, blacklisting of the sender's IP, and sender reputation affect relaying.
- Specific Platform Configurations: Issues with Google Workspace settings, Microsoft 365 accepted domains, and Postfix/Exim configurations can all trigger the error.
- HELO/EHLO Configuration: Incorrect setup of HELO/EHLO can also cause relaying denials
Key considerations
- Authentication Procedures: Implement robust SMTP authentication procedures with correct credentials and methods.
- DNS & Configuration Validation: Regularly validate DNS records, MTA configurations, and hostnames to ensure accuracy.
- Reputation Management: Monitor and maintain your sender reputation by checking against blacklists and adhering to best practices.
- Platform-Specific Settings: Carefully configure email relay settings within Google Workspace, Microsoft 365, Postfix, Exim, and other platforms following their respective guidelines.
- Error Log Analysis: Thoroughly examine error messages and logs to identify specific causes and tailor solutions.
- Leverage SMTP Relay Services: Consider using SMTP relay services to handle authentication and ensure reliable email delivery.
What email marketers say
7 marketer opinions
The '550 relaying denied' error commonly arises due to issues with sender authentication, authorization, or reputation. Solutions involve ensuring proper SMTP authentication, valid reverse DNS records, using SMTP relay services, avoiding blacklists, verifying the 'From:' address, properly configuring the hostname, and setting up the correct authentication method (like TLS).
Key opinions
- Authentication: Lack of proper SMTP authentication is a primary cause. Verify username and password configurations.
- Reverse DNS: A valid reverse DNS (PTR) record matching the sending domain is crucial for establishing trust.
- SMTP Relay: Using an SMTP relay service can bypass direct sending issues and handle authentication.
- Blacklisting: A blacklisted IP address can cause relaying to be denied; check and remove if necessary.
- Valid From Address: The 'From:' address must be a valid address associated with the sending server.
- Hostname Configuration: Incorrect hostname configuration and domain resolution problems can trigger the error.
- Authentication Method: Ensure the correct authentication method (e.g., TLS for Gmail) is set up in your email client.
Key considerations
- Authentication Setup: Carefully configure SMTP authentication settings in your email client or application.
- Reputation Monitoring: Regularly check your IP address against email blacklists to maintain a good sender reputation.
- Server Configuration: Verify the proper configuration of your mail server's hostname and DNS records.
- Relay Service Usage: Consider using a reliable SMTP relay service for handling email delivery and authentication.
- Sender Verification: Validate the sender's email address and ensure it matches the server's domain to prevent spoofing.
Marketer view
Email marketer from cPanel Forum says to check that you have the correct authentication method set up. For example, with Gmail, you will likely want to use the TLS.
9 Jun 2023 - cPanel Forum
Marketer view
Email marketer from Digital Ocean explains that this type of error can occur from issues related to the hostname not being properly configured and the local server being unable to resolve the domain.
29 Jul 2023 - Digital Ocean
What the experts say
5 expert opinions
The '550 relaying denied' error can stem from several issues: the MX server not handling mail for the recipient, DNS caching problems, incorrect MTA configurations, problems with the recipient's email provider (like Yahoo), sender authentication failures, recipient domain policies, reverse DNS records mismatching, or incorrect HELO/EHLO configurations. Error codes and logs should be checked to identify the root cause.
Key opinions
- MX Server Issues: The recipient's MX server might not be configured to accept mail from the sender.
- Configuration Problems: DNS caching issues or incorrect MTA configurations can lead to relaying denials.
- Provider Problems: Issues on the recipient's email provider's end (e.g., Yahoo) can cause temporary relaying problems.
- Authentication/Policy: Sender authentication failures and recipient domain policies can cause relaying denials.
- DNS Mismatch: Reverse DNS records not matching the mail server's address can trigger relaying denials.
- HELO/EHLO configuration: Incorrect configuration of HELO/EHLO can cause relaying denials.
Key considerations
- MX Record Check: Verify the MX records for the recipient domain to ensure proper mail routing.
- MTA Configuration Review: Carefully examine MTA configurations for any errors or incorrect settings.
- Error Code Analysis: Pay attention to specific error messages and reason codes for clues about the cause.
- Reverse DNS Setup: Ensure reverse DNS records are correctly configured and match the mail server address.
- HELO/EHLO Config Check: Validate proper HELO/EHLO configurations.
Expert view
Expert from Email Geeks confirms the VMG errors have been rolled back and advises retrying the addresses.
2 Aug 2021 - Email Geeks
Expert view
Expert from Email Geeks suggests the cause of relaying denied errors could be DNS caching issues, incorrect MTA configurations, or a problem on Yahoo's end. He recommends checking the MTA config first and examining logs for the IP address of the rejecting server.
13 Feb 2024 - Email Geeks
What the documentation says
6 technical articles
'550 relaying denied' errors typically arise due to authorization issues with the mail server or misconfigurations within email platforms. Common causes include sending emails without proper authentication, using non-accepted domains (specifically in Microsoft 365), incorrect relay settings in Postfix, and unauthorized sending IPs in Google Workspace. Utilizing dedicated SMTP relay services like SendGrid can provide a structured solution to prevent these errors. For Exim systems, detailed configuration review is essential.
Key findings
- Authorization: The mail server lacks authorization to send on behalf of the domain.
- Authentication: Improper authentication methods being utilized.
- Domain Acceptance (Microsoft 365): Sender domain not listed as an accepted domain in Microsoft 365.
- Postfix Configuration: Incorrect 'relayhost' and 'mydestination' settings in Postfix's main.cf.
- Google Workspace Settings: Sending IP address or domain not authorized in Google Workspace's email relay settings.
- Exim Configuration: Check the main configuration for Exim-based mail systems.
Key considerations
- SMTP Authentication: Always configure proper SMTP authentication when sending emails from scripts or applications.
- Accepted Domains (Microsoft 365): Add the sender's domain to the list of accepted domains in Microsoft 365.
- Postfix Relay: Review and correct the 'relayhost' and 'mydestination' parameters in your Postfix configuration.
- SMTP Relay Service: Consider using a dedicated SMTP relay service to handle authentication and prevent relaying issues.
- Google Workspace Authorization: Authorize the sending IP address or domain in your Google Workspace email relay settings.
- Exim Review: For Exim, carefully review main configuration settings.
Technical article
Documentation from Microsoft explains that if you are using Microsoft 365, this error might occur if the sender's email address is not configured as an accepted domain in your Microsoft 365 account. Adding the sender's domain to the accepted domains list can resolve the issue.
7 Oct 2023 - Microsoft
Technical article
Documentation from Google explains that you need to check your Google Workspace email relay settings. Make sure the sending IP address or domain is authorized to relay emails through your Google Workspace account.
26 Mar 2025 - Google
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