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Roundcube SMTP Error (454) Authentication Failed

by | May 27, 2021

Wondering how to fix Roundcube SMTP error (454) authentication failed? We can help you!

This error is often seen while trying to send emails via Roundcube. Here at Bobcares, we often handle requests from our customers to fix similar Roundcube errors.

Today we will see how our support engineers fix this for our customers as a part of our Server Management Services.

What causes Roundcube ‘SMTP error (454) authentication failed’

Before going into the steps for fixing this error, we will see what causes this error and how it looks like.

A typical error may look like the one given below:

SMTP Error: Authentication failure: Invalid response code received from server (Code: 454)

The following warnings will appear in the /var/log/maillog if we get this error :

Mar 20 22:13:01 postfix/smtpd[28890]: warning: SASL authentication failure: no secret in database
Mar 20 22:13:01 postfix/smtpd[28890]: warning: localhost[::1]: SASL DIGEST-MD5 authentication failed: authentication failure

Following are the two main causes for this error:

  •  Broken Postfix configuration.
  •  The pc-remote service is stopped.

Methods to fix Roundcube ‘SMTP error (454) authentication failed’

Now we will see how our Support engineers fi this error for our customers.

1. Fixing Broken Postfix configuration.

Here we will reinstall Postfix by switching to Qmail and back to Postfix.

This can the done in the following ways.

Using Plesk Installer:

The steps to follow are given below:

  1. Firstly, go to Plesk and take Tools & Settings.
  2. Then go to Updates and Upgrades.
  3. And take Add/Remove Components then go to Mail hosting.
  4. After that take SMTP servers and select the Qmail server.
  5. Next, we have to click Continue to start the installation.
  6. Once the installation is complete click Ok.
  7. Now go to Add/Remove Components and take Mail hosting.
  8. From Mail hosting go to SMTP servers.
  9. Select Postfix mail server and click Continue to start the installation.

roundcube smtp error (454) authentication failed

10. Once the installation is complete click Ok.

Using Command Line Interface (CLI):

We can use the following steps for fixing this via CLI:

  1. First, we have to connect to the server via SSH;
  2. Then execute the following commands:
# plesk installer --select-release-current --install-component qmail
# plesk installer --select-release-current --install-component postfix

2. Starting pc-remote service

This error can also occur if the pc-remote service is stopped. However, the error in the /var/log/maillog appears a little different as shown below:

warning: connect to Milter service inet: Connection refused NOQUEUE: milter-reject: CONNECT from[]: 451 4.7.1 Service unavailable – try again later; proto=SMTP

Following are the steps to fix this:

  1. First, we have to log in to Plesk.
  2. Then go to Tools & Settings and Scheduled Tasks.
  3. From there take Add Task.
  4. After that select Task Type as Run a command
  5. In the Command * field paste the line below:
/usr/sbin/service pc-remote start

6. Now we have to select root from the drop-down menu System user

roundcube smtp error (454) authentication failed 

7. Finally click the Run Now button to start the pc-remote service.

[Need assistance? We can help you]


In short, we saw how our Support Engineers fix Roundcube ‘SMTP error (454) authentication failed’ issue for our customers.


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