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Summary: Mozilla Thunderbird, a versatile desktop email client, faces common errors such as encryption issues, trash folder corruption, message deletion problems, and more. Solutions include adjusting settings and utilizing third-party tools. Kernel MBOX Viewer is recommended for efficient MBOX file management.

Mozilla’s Thunderbird stands as a widely embraced desktop email client, boasting a comprehensive array of features, including email management, newsfeed integration, chat functionality, and newsgroup support. This versatile tool is adept at handling multiple accounts and extends its availability to users on Windows, Linux, and OS X platforms. Furthermore, Thunderbird’s cost-free accessibility stems from its utilization of the open-source MBOX format for storing emails and associated data. However, like any software platform, Thunderbird is not immune to occasional technical glitches and errors.

Common Errors in Mozilla Thunderbird

While Thunderbird offers a straightforward and highly efficient experience, users might encounter occasional errors and performance issues. In the following section, we will explore some typical issues that you might come across while using Thunderbird.

1. Server Doesn’t Support Encryption

This warning typically arises when the server lacks encryption support, rendering communications with the server vulnerable to hacking attempts.

To fix this issue, try:

  • If the mail server offers encryption capabilities (refer to the help or support documentation for details), please click the “Change Settings” button to make the necessary adjustments.
  • If encryption is not supported, acknowledge the associated risk by clicking the “I understand the risk” button, and then proceed by clicking the “Create Account” button. Alternatively, consider switching to an email provider that offers a secure connection.
2. Trash Folder Corruption and Difficulty in Deleting Messages

If the Trash folder becomes corrupted, users might encounter difficulties when attempting to delete messages. To address this problem, you can rectify the situation by following the steps provided below:

  1. Access the Profile folder, then navigate to the Menu button and choose the Troubleshooting Information option.Select Help & Troubleshooting Information
  2. Next, navigate to Application Basics and select the “Show Folder” option. This action will open a window displaying the profile.
  3. Please go ahead and exit the Thunderbird application.
  4. Access the ImapMail directory for your IMAP account (or the Mail folder for a POP account).
  5. Access the directory corresponding to the incoming mail server’s name.
  6. Choose the Trash and Trash.msf files, and if they are not found, please check the Bin or Deleted folders before proceeding with deletion.Select the Trash and Trash.msf files
  7. Please restart Thunderbird, and it will automatically generate a new Trash folder. If you’re using POP, you’ll need to manually create a new Trash folder.

You can once more follow these uncomplicated steps to remove messages.

3. Unable to Receive Messages

On occasion, Thunderbird may unexpectedly cease to receive messages. Numerous factors could potentially account for this occurrence, such as:

  • ISP service status technical problems
  • Configuration problems with your account
  • ISP or Thunderbird filters

Numerous solutions can be found by reviewing the Thunderbird account settings:

  1. To access Account Settings in Thunderbird, click on the “Tools” menu and then select the option.
  2. Choose “Server Settings” from the options displayed in the left panel.Select Server Settings
  3. Please confirm the server settings in accordance with the specifications provided by the account provider.
4. Unable to Send Messages in Thunderbird

Occasionally, individuals encounter difficulties sending messages despite correctly configuring their accounts, often attributed to SMTP errors. There are various other factors that can impede the sending of email messages from a Thunderbird account. A few of these potential factors include:

  • The ISP (Internet Service Provider) has blocked Port 25.
  • Firewall and antivirus software
  • Thunderbird has entered offline mode.
  • The email service provider has implemented a captcha.
  • Incorrect Thunderbird email configuration for outgoing messages.

If you encounter these errors, we recommend consulting the Thunderbird support page on the Mozilla website for assistance.

5. Thunderbird Crash

A Thunderbird crash is an unexpected collapse of the Thunderbird email client. When this happens, you’ll typically encounter the Mozilla Crash Reporter, which will prompt you to decide whether you’d like to send crash data to Mozilla for analysis. Crashes in Thunderbird can often be attributed to problematic add-ons, but you can mitigate this problem by ensuring you regularly update your Thunderbird application.

6. IMAP Error Messages

If you’ve linked an IMAP account within Thunderbird and encounter IMAP-related issues such as ‘Unable to establish connection with IMAP Server,’ ‘failure to retrieve Thunderbird emails from the IMAP server,’ ‘excessive IMAP connections,’ and more, it’s essential to review and verify your IMAP configuration settings.

Resolution – Decrease the quantity of connections.

Numerous IMAP issues can often be resolved by reducing the quantity of connections within the Thunderbird application.

  1. Navigate to the “Tools” menu and select “Account Settings.”
  2. Within the Server Settings section, select the Advanced option.
  3. Modify the ‘cache’s maximum server connection limit’ to be set at three or fewer connections.
Mozilla Thunderbird is Not Opening

If the application’s icon isn’t launching the program when clicked, you can resolve this issue by troubleshooting Thunderbird through its safe mode.

  1. To initiate Thunderbird in safe mode, simply press and maintain the Shift key while opening the application.
  2. After launching Thunderbird, select the “Help” option and then opt for “Restart with Add-ons disabled.”
  3. Click Restart.
Kernel MBOX Viewer

Frequently encountered problems may arise from either incorrect Thunderbird settings or damage to MBOX files. When confronted with such situations, accessing these MBOX files can often be a challenging task.

It is advisable to rely on a proficient third-party tool for your email management needs.Kernel MBOX Viewer stands out as an efficient freeware solution capable of handling MBOX emails from various clients, including Thunderbird, Apple Mail, Eudora, and Entourage, among others. This tool boasts an intelligently designed interface that can preview MBOX emails from over 20 email clients without any file size limitations. Additionally, users can conveniently add multiple MBOX files for processing. Notably, the tool offers a dynamic email filtering feature, allowing users to sort retrieved emails based on criteria like sender, date/time, and folder. Another valuable feature is its ability to save email list information in HTML format, which can be easily accessed using popular web browsers such as Google Chrome, Internet Explorer, and Firefox. We highly recommend this exceptional free tool for MBOX file viewing.

Some of its unique features are-

  • The tool’s smart design allows for the preview of MBOX emails from over 20 email clients, with no restrictions on file size.
  • It has the capability to import both individual MBOX files and multiple MBOX files simultaneously.
  • The tool comes equipped with a dynamic email filter option, allowing the user to segregate the retrieved emails by selecting the criteria like From, Date/Time, Folder, etc.
  • It has the capability to store email list data in HTML file format, facilitating effortless accessibility through widely-used web browsers like Google Chrome, Internet Explorer, and Firefox.
  • You can view MBOX files completely free using this tool.


The blog delved into common errors associated with the Thunderbird email client, their likelihood of occurring, and provided primary solutions for each issue. Recognizing the significance of safeguarding MBOX file data from Thunderbird-related errors and the need for a quick solution, it introduced the free, professional utility known as Kernel MBOX Viewer. This tool enables users to access and view their MBOX file data, and it was complemented by an explanation of its additional benefits for users.

Kernel for MBOX to PST