Repair Thunderbird Folder Index (MSF) Files with ThunderFix

Mozilla Thunderbird is perhaps the most popular open source email client in the world. It is available for all the popular platforms – Windows, Mac and Linux alike. In fact, Thunderbird comes pre-installed in all the Linux flavors like Ubuntu and Mint etc. Thunderbird has become so popular because it has been built along the same principles of the security and flexibility as its sister product Mozilla Firefox. Once installed and configured, Thunderbird keeps working without any problems except when the files become corrupt due to power outage, system crash or malware attack.

When the Thunderbird folder index files (.MSF) files become corrupt, messages may appear more than once, they become missing, keep re-appearing even after you delete them or get deleted automatically. In order to fix these problems, you can delete the MSF files from Thunderbird profile and the next time you start Thunderbird, it re-creates them. You can do it manually, but a free tool ThunderFix can do it automatically for you.

To fix the MSF file problems you have to download, install and launch ThunderFix. Then  you have to select the Thunderbird profile from the list that you want to fix. Most of the users will have only one “default” profile. As soon as you select a profile, it will calculate the number of MSF files in that profile. Now you can click on the Fix Profile button to delete these files. Do not forget to close all the running Thunderbird instances before proceeding.


A confirmation prompt is displayed after which it continues to delete the files. It does not take much time to delete the MSF files and only in 1-2 seconds, you will be shown a message informing you that everything has been done successfully. Now you can start Thunderbird email client and it will re-create fresh MSF files.


Conclusion: Corrupt index files (.MSF) in Thunderbid can cause unexpected behavior for email listings for various email accounts. You can fix these either manually or through the free ThunderFix tool.

You can download ThunderFix tool from

One comment

  1. This is useless tool. All (one) functions – deleting msf-files.

    More usefull – to check mbox-format. I’m manually repaired mbox (320 megabytes) after BSOD with several error like this:
    ————————-start error block at line 288991—————-
    From – Fri Apr 02 01:07:57 1999

    From – Fri Apr 02 01:07:57 1999
    X-Mozilla-Status: 8001
    ————————-stop error block—————-

    Eye search – difficult.

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