If you tried sending an email but got the “550 5.7.367 Sender Not Authorized for Relay“ error pop-up, you’ve come to the right place. Only a person failing to send an important email can understand how exhausting this error can be. But you are not alone in this! The “sender not authorized for relay” error is usually triggered when the receiver’s email server doesn’t recognize you as an authentic sender.

Fixing the issue is essential to prevent email deliverability issues. This article will break down what this error means, the possible reasons, and most importantly how it can be resolved effectively. Read on to know more!

Key Takeaways

Understanding the Error: The “550 5.7.367 Sender Not Authorized for Relay” error occurs when the sending server is not recognized as an authorized relay.
Common Causes: Misconfigured SPF, DKIM, or DMARC settings, incorrect SMTP authentication, IP blocklisting, and restrictive email server configurations can trigger this error.
Recognizing Symptoms: Signs include email bounces with relay error messages, inconsistent email delivery, and emails being marked as spam or undelivered.
Troubleshooting Steps: IT admins should verify server settings, update authentication protocols, check blocklists, and test SMTP configurations; users should identify the issue’s scope, communicate with recipients, and forward error reports.
Preventive Measures: Regularly updating mail server configurations, using authorized SMTP servers, and properly implementing DMARC, SPF, and DKIM can help avoid relay issues.
Persistent Issues: If the problem continues, escalate it to IT teams, contact the recipient’s email support, or consider third-party security solutions for better email authentication and deliverability.

What Is “Sender Not Authorized for Relay”?

You may have received an error while sending an email that reads “Sender Not Authorized for Relay”. As the name indicates, the error occurs when the person trying to send an email is not authorized to send relay emails through the server.

A relay is a mail server through which email messages are sent from server to server until it reaches the user’s mailbox. An open relay is an unauthenticated mail server through which emails are sent without any authentication. The security of these servers is almost zero. Therefore they are more prone to cyberattacks.

However, a restricted relay allows only authenticated emails to pass the servers. Therefore, users receive an error “Outlook sender not authorized for relay” when they try to send emails through these servers.

Common Causes of “Sender Not Authorized for Relay” Errors

The main reason behind the error is the lack of proper authentication. But, it can also be due to various causes.

1. SPF Record Issues

If your sending IP is not included in your domain’s SPF record, it can lead to “Sender Not Authorized for Relay” error. During SPF authentication, receiving servers check your domain’s SPF records to confirm your authorized senders. In case your sending IP is not listed in this record, it will be deemed unauthorized and lead to SPF failure.

2. DKIM or DMARC Failures

DKIM or DMARC failures can lead to the “Sender Not Authorized for Relay” error when strict authentication policies are enforced. DKIM may fail due to misconfiguration, missing DNS records, or email modification in transit. Additionally, if the domain’s DMARC policy is set to “p=reject”, any email failing SPF and DKIM alignment will be blocked, preventing unauthorized senders from relaying messages.

3. Incorrect Email Server Configurations

The incorrect email server configurations range from SMTP relay issues to outdated server sessions. You may receive this error if you have not updated the authentication protocols of your email server. Configuration settings including incorrect port numbers can also lead to this error.

4. IP Blocklisting and Domain Restrictions

The email service providers can block an IP address or add a domain to the blocklist causing trouble. The domains that have been blocklisted by the ESPs will not be able to relay messages.

Other than this, some domains impose strict restrictions to allow only authenticated users to send emails on their behalf. You can also check if your domain has been blocklisted with the help of DNS and IP blocklist monitoring tools.

5. Misconfigurations in SMTP Authentication

SMTP servers require authentication to verify that the sender is authorized to send emails through them. If authentication settings are incorrect, the server will reject the email, leading to a “Sender Not Authorized for Relay” error. This can happen when senders use improper username or password combinations, or if the email client is not set up to use authentication.

6. Sending from a Different Network

Some email service providers restrict SMTP relay access to only users connected to their own network. When trying to use a different network to relay messages the SMTP server may block the activity in its tracks for security purposes.

Recognizing the Symptoms and Impact of Relay Errors

These relay errors not only cause trouble sending emails but also hinder communication and workflow. Here is how you can recognize the “550 5.7.367 Sender is Not Authorized for Relay” error and its impact on email communication.

Tell-tale Signs of Relay Errors

1. Increased Email Bounces with Error Codes

You receive an email failure notification with messages like:

“550 5.7.1 Unable to relay”
“Relay access denied”
“Sender not authorized for relay”

2. Inconsistent Message Delivery

You can predict the error if the emails are not falling into a specific inbox and other addresses are working fine. This selective failure of the emails shows that there are restrictions between the sender’s and receiver’s email servers.

3. You Can Receive but You Can’t Send

If you are receiving emails just fine yet you can’t send them, or your emails suddenly start failing when they were working just fine before – it can be a relay issue.

4. Emails Being Marked as Spam or Undelivered

If you have incorrect SPF, DKIM, and DMARC records configured for your domain, it can lead to messages being flagged or rejected.

User Impact

The relay errors can affect communication by blocking important email messages. This may affect business by restricting important emails from falling into the user’s inbox. If these issues are not timely addressed, they affect the email system and cause major losses. Here is a summary of issues users may face as a result of this error:

Increased email bounce rates
Poor email deliverability
Increase in email spam rates

Key Statistics and Examples of User Impact

In 2024, spam emails constituted approximately 47.27% of total global email traffic, marking a 1.27 percentage point increase from the previous year.
Daily Spam Emails: An estimated 160 billion spam emails are sent daily, accounting for 46% of the 347 billion emails transmitted each day in 2023.
In 2024, the average email deliverability rate across major email marketing platforms was 83.1%, indicating that nearly one in five emails failed to reach recipients’ inboxes.
More than 10% of emails sent ended up in subscribers’ spam folders, highlighting the importance of proper authentication and sender reputation.

Troubleshooting “550 5.7.367 Sender Not Authorized for Relay” Error

Whether you are an IT administrator or a user trying to relay email through your domain, here’s what you can do to get rid of “sender not authorized for relay” errors:

For IT Administrators

IT professionals trying to tackle this error may take the following steps:

1. Verify Email Server Settings

Firstly, check the SMTP server settings. Make sure the settings are correct. The major settings that need to be checked include port numbers, server addresses, and updated authentication protocols. Keep checking and updating server settings according to the changing rules.

2. Check and Update Email Authentication Protocols

The updated email authentication protocols play a major role in the smooth functioning of the email relay system. The authentication protocols essential to prevent relay errors are DMARC, SPF, and DKIM. Properly configure these authentication protocols to authenticate your outgoing emails.

3. Inspect Blocklists and Whitelists

You must also verify if your domain has been blacklisted by ESPs. You can do this with online DNS checker tools. You can take measures to remove your domain from the blocklist if it is blocked. You must also whitelist the user’s IP addresses to prevent the failure of emails.

4. Test SMTP Configuration and Relay Permissions

Check the proper configuration of SMTP relay permissions. The settings must be done to allow authenticated users or serve to relay emails easily. Use online testing tools to stimulate email sending.

For End-Users

Users can also take steps from their end to prevent the error from ruining their email communication. Here are the steps that be taken to resolve the error:

1. Identify the Scope of the Problem

The first thing you need to do is to identify the error. You can do this by determining if the error occurs while sending emails to all the recipients or just a specific one. This makes it easy to diagnose the error. Users will be able to understand if the error is occurring on their domain or the recipient’s side. To further isolate the issue, try sending emails from different mail clients, as some errors may be specific to certain email applications or their configurations.

2. Communicate with Recipients

Communicate with the recipient if the error occurs after sending emails to a specific domain. The recipient’s inbox might have restricted the incoming emails. Ask the receiver to add your domain or email address to their trusted list.

3. Forward Error Reports to IT Teams

Each error has a specific meaning that you can read here: “SMTP Error Codes Explained“. If you are unable to understand the cause behind the error, share details with the IT professional. The details must include the error message, timestamp, and recipient’s address.

Preventing Future Relay Issues: Best Practices

Fixing the relay issue once is not enough. You need to take preventive measures to make sure it doesn’t happen again. Regularly monitor your SMTP logs, implement strong authentication protocols, and keep your mail server software up-to-date. Additionally, educate your users about proper email security practices and configure mail clients correctly to prevent unauthorized relay attempts.

1. Keep Mail Server Configurations Updated

The email configuration settings must align with the changing trends and policies This is essential in preventing errors. Updating the mail server settings timely reduces the risk of misconfigurations and errors.

2. Use Authorized SMTP Servers Only

Use authorized servers to make sure your relay email doesn’t get scammed before reaching the recipient’s inbox. Verified SMTP servers minimize the email rejection risks. Configure your remote server to use secure authentication methods for SMTP relay.

3. Implement Authentication Protocols Correctly

Authenticate your ongoing emails with DMARC, SPF, and DKIM protocols. If you are unsure about setting these up correctly, you can use a DMARC solution to automate the process for you!

What to Do if the Issue Persists

What if after trying everything the issue persists? You can take the following measures:

1. Escalating to IT Teams

Forward the issue to your IT department if you are unable to fix the error. There are some tools designed to track and fix the DNS-related settings. IT professionals use such tools to resolve the issue.

2. Contacting the Recipient’s Email Support Team

Sometimes, your domain is just fine. The error can occur from the recipient’s side. Contact the recipient and collaborate with their email support team to identify the issue.

3. Consider Third-Party Security Services

Use advanced filtering, authentication, and monitoring features to resolve the persistent issue. Using authentic third-party services also increases the deliverability of the emails.

Endnote

The error “550 5.7.367 Sender Not Authorized for Relay” is one of the common email relay errors. The issue is resolvable and can be prevented with essential measures. Efficiently maintaining email authentication protocols, reviewing your server settings, and using tools to recognize and fix email relay errors can help ensure reliable email communication.

About
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Ahona Rudra

Domain & Email Security Expert at PowerDMARC

Ahona is the Marketing Manager at PowerDMARC, with 5+ years of experience in writing about cybersecurity topics, specializing in domain and email security. Ahona holds a post-graduation degree in Journalism and Communications, solidifying her career in the security sector since 2019.

Fix “550 5.7.367 Sender Not Authorized for Relay” Error Message