Postfix Relay Access Denied: How to Fix

In our daily life, we rely on emails for quick and efficient means to convey our messages. Whether you belong to education or a professional sector, you must have used some sort of email service to conduct your business.

With almost 320 billion emails sent and received daily, according to the statistics, it’s clear that any hindrance in this means of communication is abhorrent. That said, email services aren’t immune to errors and failures.

Many users often face an error message known as “Relay Access Denied” when using the default mail transfer agent in Ubuntu, Postfix, developed by IBM. This guide will dissect this error message to identify its potential causes and solutions. So, without further ado, let’s get started.

What Is The Postfix Relay Access Denied?

To understand how email communication works, you must be familiar with the mail servers and clients. Each sender and receiver acts as a client with a central server that relays the emails shared between these clients.

For instance, if you use Outlook as your mailing service, your inbox or sent box is your client, whereas the mailing box of Outlook is their server. While carrying out this regular email flow in the Linux services, users sometimes receive a Postfix Relay Access Denied error.

This error can pop up if the sender’s email server fails to relay the sent email to the recipient’s email server. Alternatively, another cause for the error is the mail server of the recipient rejecting the incoming email from the mail server of the sender.

In either case, the sent email doesn’t get delivered to the recipient, hampering the relay of information. Depending on the urgency of the information, getting such an error in your communication can be harmful to your company.

Therefore, knowing the potential causes and troubleshooting methods would help you a ton in carrying out your business.

Causes For The Postfix Relay Access Denied Error

Before jumping on to fix the Postfix Relay Access error, you need to diagnose the root cause of the issue. Common causes for the “Postfix Relay Access Denied” error message are listed in the sections below:

• Sender’s Mail Server Rejects The Email Due To Authentication Issues

In order to prevent spam emails, each email sent through the sender has to be authenticated with a username and password.

So, whenever Postfix fails to authenticate an email due to incorrect credentials or the authentication service being turned off, the sender mail server rejects the email with the Relay Access Denied message.

• Receiver’s Mail Server Rejects The Email Due To Misconfiguration

Once the email has been successfully relayed to the recipient’s server, it could reject the email in case the sender’s mail server doesn’t pass the spam filters or it has some misconfigurations.

Issues like an invalid recipient email, SMTP authentication disabled, database faults in the sender’s mail server, and wrong DNS records would result in a rejection from the recipient’s side.

Troubleshooting the Postfix Relay Access Denied Error

Now that you’re familiar with the reasons behind the “Postfix Relay Access Denied” error message, let’s explore its troubleshooting techniques. We will look at the troubleshooting methods in cases where the sender or the recipient’s mail server rejects the email.

Postfix Relay Access Denied On The Sender’s Side

In case your email is being rejected by your own server, it is most likely an authentication problem. Contact your mailing service provider and verify your credentials, your spam filters in case your email is being tagged as spam, and the authentication of your SMTP protocol.

Some email services also use the Post Office Protocol (POP) to retrieve emails from the mail server. POP often runs into network issues if you’re using more than one device with different IP addresses or Internet Service Providers (ISPs).

Therefore, you can ask your mailing service to switch your authentication from POP to SMTP instead.

Postfix Relay Access Denied On The Mail Server’s Side

If the Postfix Access Denied error is being generated on the mail server’s side, then it’s an entirely different issue. Let’s discuss various scenarios that may be at the backend of this problem and how to resolve them.

1. User Authentication Failed

One of the most common reasons for the Relay Access Denied error on Postfix servers on the mail server’s side is the failure to authenticate the end users.

In order to combat this issue, you need to review your authentication configuration on the Postfix server and make sure that SMTP authentication of the users is enabled.

1. Log in to your cPanel account and go to your configuration files.
2. Open the configuration file titled smtpd_recipient_restrictions.
3. Change the configuration of this file as smtpd_recipient_restrictions = permit_sasl_authenticated”.

Doing so will fix the issue of user authentication at the server end. Since cPanel tends to install new updates on the server automatically, your default configurations can be changed after the latest updates.

Therefore, if you run into an error on a functioning server that halts its operation, it is more than likely that a new update has changed some configuration. To deal with this issue, you can opt for manual updates.

2. Corrupted Database

If the database containing the user-authenticated username, passwords, and IP addresses becomes corrupted, the email server will reject any incoming queries. Therefore, knowing how to restore the database would fix this problem.

1. Open your SQL server.
2. Run the command mysqlcheck -r psa smtp_poplocks -uadmin -p to restore the smtp_poplocks table containing the userdatabase.

Once the table has been fixed, the normal server functionality will be restored.

3. External Mail Service Error

When the sender uses a different email service than the recipient, the spam filter incompatibility can often cause some issues. However, we have some quick and easy ways to resolve the external mail service spam filter problems.

Check your mail logs to ensure emails from trustworthy email services and addresses aren’t being blocked. Whitelist the email servers in Postfix which are trustworthy to ensure no valid email is falsely flagged as spam.

Ask the sender to reconfigure their anti-spam filters.

Postfix servers have anti-spam filters enabled by default. However, false flagging of emails is a common problem, and a proper reconfiguration of all the spam filters and checks would help resolve the “Postfix Relay Access Denied” error in this case.

Conclusion

We hope this guide has given you a straightened and linear concept of the “Postfix Relay Access Denied” error message. Dealing with email issues can be frustrating, especially when quick and urgent information reliance is needed.

However, with the fixes described above, you’ll be able to resolve any message relay problems on the Postfix servers.