Some Common Errors You May Encounter in Thunderbird

Siddharth Rawat
Siddharth Rawat | Updated On - 02 Mar 2021 |

Read time 5 min

Mozilla’s Thunderbird is a popular desktop-based email client that offers a bundle of facilities like email, newsfeed, chat, newsgroup, etc. It is designed to manage multiple accounts, and is available for Windows, Linux, and OS X platforms, Moreover, it is free (Thunderbirds uses MBOX format, a free open source format, for storing its emails and other data.)

Mozilla Thunderbird Errors

Though Thunderbird is very simple and extremely efficient, users may occasionally face some errors and performance issues. Here, we will discuss some common Thunderbird issues.

1. Server Doesn’t Support Encryption

This warning generally occurs when the server doesn’t support encryption (making the communications with the server vulnerable to hacking).

To fix this issue, try:

  • If the mail server supports encryption (read help/support documents for this information), click Change Settings button and modify the settings.
  • If it doesn’t support encryption, check I understand the risk and click the Create Account button and proceed. Alternately, you can switch to mail a provider that offer secure connection.

2. Trash Folder Corruption and Difficulty in Deleting Messages

When the Trash folder is corrupt, users may not be able to delete the messages. You can resolve this issue by following the steps below:

  1. Open the Profile folder, go to the Menu button, and select Help > Troubleshooting Information. Select Help & Troubleshooting Information
  2. Now, under the Application Basics, click Show Folder. A window with the profile opens.
  3. Now close the Thunderbird application.
  4. Open the ImapMail folder for IMAP account (Mail folder for POP account).
  5. Open the folder with the name of the incoming mail server.
  6. Select the Trash and Trash.msf files and delete them (if you don’t find check Bin or Deleted).Select the Trash and Trash.msf files
  7. Now, restart Thunderbird. A new Trash folder will be created automatically (in the case of POP, you will have to create a new Trash folder).

These simple steps will again allow you to delete messages.

3. Unable to Receive Messages

Sometimes, Thunderbird might stop receiving messages suddenly. There could be various reasons behind it like,

  • Technical issues with ISP service status
  • Account configuration issues
  • Filters with ISP or Thunderbird

Many of these issues be resolved by checking the Thunderbird account settings:

  1. In Thunderbird, select Tools and then go to Account Settings.
  2. Select Server Settings from the list that appears on the left panel.Select Server Settings
  3. Now verify the server settings (according to specifications given by the account provider).

4. Unable to Send Messages in Thunderbird

Sometimes, users many not be able to send messages even after configuring the account properly. It may be due to SMTP errors. Also, there could some other reasons which restrict sending email messages from Thunderbird Account. Some are:

  • Port 25 blocked by the ISP Internet Service Provider
  • Firewall/ antivirus program
  • Thunderbird is in offline mode
  • Captcha set by the email service provider
  • Inappropriate outgoing mail settings in Thunderbird

In case of these errors, it is suggested that you refer to Thunderbird support page on Mozilla website.

5. Thunderbird Crash

Crash means unanticipated Thunderbird collapse. When the Thunderbird email client crashes, the Mozilla Crash Reporter would appear asking you whether you want to send the crash information to Mozilla for processing or not. Thunderbird crash can occur due to problematic add-ons. This issue can be rectified with regularly updating your Thunderbird application.

Kernel MBOX Viewer

Some of the common issues can be due to improper Thunderbird settings or MBOX file damages. In such a scenario, it is often difficult to view these MBOX files.

Therefore, it is recommended to always rely on a proficient and nifty third-party tool. Kernel MBOX Viewer is an efficient freeware tool that can be used to view Thunderbird, Apple Mail, Eudora, Entourage and more MBOX emails. The intelligent design of the tool can preview MBOX emails of 20+ email clients with no limitation on the file size. Another essential feature of the tool is that one can add multiple MBOX files. The tool comes equipped with dynamic email filter option, allowing the user to segregate the retrieved emails by selecting the criteria like From, Date/Time, Folder, etc. One added advantage of the tool is that it is capable of saving email list information in HTML file format, which can be easily accessed with popular web browsers such as Google Chrome, Internet Explorer and Firefox. We highly recommend this absolutely free tool for viewing MBOX files.

Download Software


The blog was settled down with the Thunderbird email client-related common errors with their chances of occurrences and the linked primary solutions to each of them. Knowing the importance of the MBOX files information on inaccessibility due to Thunderbird errors and in times of urgency, a free professional utility Kernel MBOX Viewer tool to view MBOX files data was introduced along with the mention of additional advantages for user’s benefits.