Postfix Relay Access Denied

Before going into depth about finding the causes for Postfix Relay Access Denied error messages, we will first try to find out what this message means. To determine the meaning of this message, we must first know how emailing works. Let us assume that a sender A wants to send an email to a recipient B. As soon as sender A sends his email, the message will first be sent to sender A’s mail server. Then, this email will be relayed to recipient B’s mail server. Finally, the email is delivered to recipient B’s mailbox.

This is the regular flow of this process. However, if sender A’s mail server rejects to relay the email to recipient B’s mail server, or if recipient B’s mail server rejects to accept the incoming email from sender A’s mail server, then sender A will receive the Postfix Relay Access Denied error message. This article will explore all the potential causes of this error message.

Common causes for the Postfix Relay Access Denied error message are listed in the sections below.

Authentication Issues at Sender’s Mail Server

The Postfix Relay Access Denied error message is generated whenever a Postfix mail server fails to authenticate the sender. This commonly occurs when the sender’s authentication is turned off by default in his mail client and the sender forgets to turn it on before sending the email. To avoid this issue, the sender must ensure that the authentication in the email client is enabled before attempting to communicate with anyone.

Invalid Recipient

The recipient’s mail server will only accept an email from another server when that email is meant for a valid recipient, i.e., the requested recipient’s entry exits on the mail server. However, if the recipient’s account no longer exists or is currently inactive, then the recipient’s mail server will fail to relay this message to the recipient’s mailbox, and this will give rise to the error. To avoid such situations, you must ensure that the recipient that you want to contact is a valid user.

Server Migration Issues

A server cannot stay as it is for its entire lifetime. Server migration is very common, especially for virtual servers. Server migration is the process by which a virtual server is moved from its original physical server to another physical server. The address used to access a certain server may change, and the server may no longer be accessible from the same address. If you try to contact a server that has already migrated to another destination, then you will get the Postfix Relay Access Denied error message. You can prevent this situation by ensuring that the address to which you are trying to contact the mail server is the server’s present valid address and that it has not migrated to any other location.

Altered User Database

At times, the user-related information on a mail server is maintained in the form of a database. If this database is attacked by a hacker or virus and the records are damaged, you will receive the Postfix Relay Access Denied error message. This happens because the mail server no longer has valid records to compare the sender and receiver credentials and, as a result, authentication issues arise. To prevent this from happening, you should apply all the relevant database protection mechanisms for keeping your critical data safe from any unauthorized access, modification, or deletion.


This article provided some useful information about the Postfix Relay Access Denied error message. We first learned what this error, in reality, is by relating it with an example. Then we looked at some of the most important causes which give rise to this unwanted situation. Along with these causes, we also discussed various measures to take to avoid this error from occurring. If you can manage to take care of these little tips before using Postfix for sending and receiving emails, you can surely prevent yourself from facing this issue, making your communications even faster and without getting yourself into any trouble.

About the author

Karim Buzdar

Karim Buzdar holds a degree in telecommunication engineering and holds several sysadmin certifications. As an IT engineer and technical author, he writes for various web sites. He blogs at LinuxWays.