How to Fix ‘no valid MBOX files were found’ Error on Mac

Written By

Published on
October 18th, 2021

Updated on
October 23, 2021

5 minutes Read

Summary: If you are facing no valid MBOX files were found error was found on your Mac, stick here with this post. Here we will provide you some of the causes behind the error and the best possible way to fix them manually. Also, we will describe the step-by-step process to convert Thunderbird emails to different file formats and email clients using the Mac MBOX Converter Tool.

Download MacSonik MBOX Converter

MBOX is a file format widely supported by email clients such as Thunderbird, Apple Mail, Opera Mail, SeaMonkey, etc. It is a file format that stores a collection of electronic mail messages. Unfortunately, nothing is perfect, so the Thunderbird is not perfect. Sometimes, no valid MBOX files error due to which they’re unable to open their Thunderbird file.

Before proceeding further, firstly, know the causes behind this error and after that, move forward to perform the steps that might help you to fix the error.

Causes of No Valid MBOX Files Were Found

There are several instances where users encounter the no valid MBOX file error. Some of them are listed below:

  • Compatibility Issue: If the user tries to open the MBOX file in different versions of macOS, they might face this problem.
  • Damage or Corrupt Storage Device: The error arises due to the corrupt or damaged external storage space that contains the MBOX file.
  • Corrupt MBOX File: If the user wants to open a corrupt MBOX file due to a virus attack, sudden termination, or improper formatting.

In the above section, we have described some of the common causes that are causing the error. Now, let’s proceed further and find the best possible ways to fix the error in MBOX Files that lead to problems i.e. no valid MBOX files found.

How to Fix No Valid MBOX Files Were Found an Error?

After identifying the causes of the problem, it is easy for you to understand the problem that displays the error. Here we will provide different methods to solve the issue effortlessly. Also, we will provide a professional way to fix the error.

Method 1: Open the MBOX file Using Thunderbird Email Client Manually

In this section, we will discuss the step-by-step process to import an MBOX file on Mac using Thunderbird. It requires the installation of some add-ons to carry forward the import process. After installing the ImportExportTools, we can proceed further to import the MBOX files to Thunderbird Manually.

  • Open the Mozilla Thunderbird on your macOS.
  • Navigate the Tools tab and expand the ImportExport option to choose the Import MBOX file.

Fixing ‘no valid MBOX files were found’ on Mac

  • Choose the MBOX file and click on the Open button.

Convert MBOX file

  • In the wizard, select the Import directly one or more MBOX files option.

No valid MBOX files were found

  • Now your MBOX file is imported into the Local folder of Thunderbird mail.

Apple mac mail MBOX converter

  • At last, you can View your Imported MBOX files items.

convert mac mail to pdf

Here your MBOX files are successfully imported into the Thunderbird local folder. You can also view and open your MBOX files into different email clients and file formats using the professional method. In the below section, we have described the step-by-step procedure to remove no valid MBOX files were found error.

Method 2: Professional Mac MBOX converter Utility

MacSonik MBOX Converter Tool is the virus-free and most trusted utility that converts the MBOX file into different file formats such as PDF, PST, EML, CSV, TXT, HTML, etc. It also allows the users to import MBOX files into Gmail, Outlook, Yahoo, Office 365, and many more on macOS.

Steps to Convert MBOX File Using MBOX Converter Tool

  • Download and Run MacSonik MBOX Converter Software.
  • Choose the conversion mode Single/Multiple.
  • Tap on the Browse button to add the MBOX file and press the Open button.
  • Tick the Folder from the tree structure. Here you can also Preview the select MBOX files item.
  • Choose the Saving file format or email client from Save/Backup/Migrate As option.
  • Now, opt for the additional features as per your requirements.
  • Click on the Path to save button and assign a location for the resultant file.
  • Finally, click on the Convert button to start processing the conversion process.

Some Attributes of MBOX Converter Software

  • The software supports all types of MBOX files such as MBX, MBS, and MSF on macOS.
  • It converts Mac mail to PDF, PST, EML, EMLX, MSG on macOS.
  • Allows users to export MBOX files into different email clients such as Office 365, Gmail, Yahoo, Outlook, IMAP, etc.
  • Users can migrate MBOX files in bulk by using multiple conversion modes.


At last, we would like to say that no valid MBOX files were found faced by many Mac users while trying to open the MBOX file. In the above post, we have mentioned all the manual approaches. However, in some cases, this approach doesn’t work. In that case, users can opt for the professional way that allows the users to convert MBOX files to Outlook and other different file formats & email clients. Thanks for reading this article.

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