Read time 4 minutes

Summary: Users of MBOX email clients, like Mozilla Thunderbird, often face the “greyed out” MBOX file issue, preventing MBOX import. This article discusses the problem’s causes and offers solutions. It also recommends Kernel MBOX Viewer, a free tool for viewing MBOX files, and highlights its features and benefits.

MBOX email client users, such as those using Mozilla Thunderbird, frequently encounter problems with MBOX files that can disrupt their email communication. Among these issues, the most prominent one currently is the “greyed out” MBOX file problem. In this discussion, we will delve into this particular issue with MBOX files.

What is The “Import MBOX Greyed Out-File Issue”?

Mozilla Thunderbird, a widely recognized desktop email client, utilizes the MBOX/MBX format to store emails. However, MBOX files are not immune to corruption and various problems. A common challenge encountered by numerous users is the “MBOX Greyed Out-File Issue,” which prevents them from importing MBOX folders into the Thunderbird application. This situation, where the MBOX file appears greyed out, leads to complications in accessing emails.

The error usually comes with the following error message:
Cannot Import messages: "The Import Messages from a Directory" is Light Grey.

This error can occur due to a variety of reasons, including the presence of corrupted, damaged, or broken MBOX files, the intrusion of bugs into the email client, failure to update the application, conflicts with other software, and the absence of necessary files in the directory.

Some Basic Solutions for “Import MBOX Greyed Out-File” Issue

In this context, we offer several solutions that you can implement promptly upon encountering the “Import MBOX Greyed Out-File” error.

  • Exit Thunderbird, relaunch the application, and attempt to import the MBOX file once more.
  • Examine the MBOX file’s directory organization, with a particular focus on its header.
  • Consider upgrading your Thunderbird application to the most recent version that is currently available.
  • Deactivate add-ons and any other software applications that are triggering conflicts.
Try a Professional MBOX Viewer Tool

If you wish to access the content of an MBOX file, consider using a proficient MBOX Viewer tool capable of displaying your MBOX files. Kernel MBOX Viewer is a free viewer tool that can read, open and view MBOX files data. It provides compatibility with over 20 MBOX email clients, including the Mozilla Thunderbird email client.

Functions and Benefits Offered by Kernel MBOX Viewer
  • Completely cost-free for everyone.
  • Access and view emails stored in MBOX files.
  • There are no limitations on file size when it comes to MBOX files.
  • Showcases MBOX emails alongside their associated metadata.
  • Intuitive and engaging Graphic User Interface.
  • Preserves the email structure within the MBOX file.
  • Stores the list of retrieved MBOX emails in HTML format.
  • Provides compatibility with approximately 20 email clients, including Eudora, Thunderbird, AppleMail, SeaMonkey, and more.

To gain a comprehensive grasp of the functionality of the free Kernel MBOX Viewer tool, let’s explore the key steps in its operation.

  1. Download the tool from and install it in your system.
  2. Choose the MBOX email client from the welcome screen.MBOX Viewer tool Home Screen
  3. Next, incorporate the MBOX files by selecting the appropriate button.Add MBOX files
  4. All mailbox data, encompassing every mailbox folder, will be presented for your perusal. Simply click on any MBOX mailbox folder to access a comprehensive preview.View MBOX file

Therefore, using this tool makes it effortless to access, read, and view MBOX files without the need for an MBOX email client.


Import MBOX Greyed Out-File’ issue restricts MBOX email client users from importing MBOX files into the Thunderbird application. If the problem is not substantial, you can consider employing a few simple manual fixes. However, if the issue proves to be more challenging, using a professional MBOX viewer tool may be the most effective solution.

Kernel for MBOX to PST