Fix Slow Or Hanging Thunderbird Email Client

Martin Brinkmann
May 19, 2009
Updated • Jun 29, 2017
Email, Thunderbird

The following guide provides you with instructions on fixing the Thunderbird email client when it becomes slow or hangs regularly.

Thunderbird is a desktop email client that is seen by many as a viable alternative to Microsoft Outlook on the Windows operating system. Users who use the client heavily, may experience slow downs or lags when using the desktop email client after some time.

This can usually be attributed to corrupt msf files in the Thunderbird profile folder. Thunderbird stores the emails in a file without file extension that has the same name as the folder name in the email client, for instance inbox for the inbox folder.

Each of these files contains the emails of the specific folder. Each folder has a msf file associated with it that is an index of all emails stored in that folder.

Repairing Thunderbird Folders

repair folder

Thunderbird comes with its own repair functionality built-into the email client. Do the following to use it:

  1. Right-click on the folder that you want to repair and select properties from the context menu. This opens the Folder Properties window. Note that this works only for folders, but not for entire email accounts.
  2. Locate and activate the Repair Folder button there. It should be visible right away, but if Thunderbird opens a tab you don't see it listed on, switch to the general information tab to locate it.
  3. I suggest you wait until the repair operation completes before you do anything else. Repeat the steps for any other folder in Thunderbird.

Fixing Thunderbird slow downs

thunderbird msf files fix slow downs

The problem is that these indexes can become corrupt over time which may cause the slow downs and hangs that some user experience in Thunderbird.

The easiest way to fix this problem is to delete the msf files in the Thunderbird profile folder after closing the Thunderbird email client. Thunderbird will automatically rebuild the indexes on its next startup fixing any problems that were caused by these files.

The easiest way to access the profile is by selecting Help > Troubleshooting information in Thunderbird, and there on the page that opens the "show folder" button. This opens the local profile folder

Note: It is of course recommended to backup the Thunderbird profile folder before deleting any files within (Check Backup Email Clients And Web Browsers).


Another possibility is to run a software program like ThunderFix. ThunderFix eliminates most of the hassle associated with the process.

It displays a list of Thunderbird profiles that it found on the computer system after execution. All it takes to delete all msf files associated with the profile is to select the profile and click on the Fix Profile link.

It is again recommended to backup the profile before running the software program.

While you may find that this is a viable solution for some slow down issues or freezes in Thunderbird, you may want to take a look at other possible solutions that help you speed up the email program on your system.

  1. Make sure you have configured Thunderbird to compact the mailboxes regularly to save space. You can do so under Tools > Options > Advanced > Network & Disk Space > Compact all folders when it will save over xx MB in total.
  2. If you do not rely on the global search, or notice that it slows down the email program, you may want to consider disabling it. You find that option under Tools > Options > Advanced > General > Enable Global Search and Indexer.
  3. If you are running add-ons in Thunderbird, try disabling those manually via Tools > Add-ons, or use Help > Restart with Add-ons Disabled to restart the email client with all extensions disabled for that session.
Fix Slow Or Hanging Thunderbird Email Client
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Fix Slow Or Hanging Thunderbird Email Client
The following guide provides you with instructions on fixing the Thunderbird email client when it becomes slow or hangs regularly.
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  1. Ness Blackbird said on August 18, 2021 at 4:14 am

    Well, this was very useful to me…it got me going…first, I tried to run the repair on my Inbox, but it turned out to be so big that it took forever to run. So I took a lot of messages out of it, and put them on the Local Folders.

    The problem persisted, but the hangs didn’t last as long. I did succeed in repairing the folders, but I don’t know if that mattered. I think the main thing I did was just to uncheck “Select this folder for offline use” under Synchronization. Since I did that, the slowdown is gone. So far, anyhow ;)

  2. Anonymous said on January 14, 2021 at 12:33 pm

    This fixed my issues thank you.

  3. wwww said on April 3, 2020 at 11:22 am

    BTW my problem is on mac Mojave. The hang is indefinite, it’s not just “slow”.
    BTW2 it’s crazy that these problems have not been solved since 2008.

  4. wwww said on April 3, 2020 at 11:19 am

    I have TB hanging very frequently. Often I can see (with Tablauncher, which shows the active windows as poststamps) that TB has multiple windows “open” in the background, but invisible to me, they are not on the screen..

    Sometimes when I selct “force quit”, it comes back to life just before I confirm the quit. Often it’s showing me a password prompt. This leads me to believe that one of the bugs involves prompting for a password which goes wrong, which then locks out all TB windows.

  5. Anonymous said on August 14, 2018 at 11:30 pm

    good stuff. thanks
    got me out of a jam

  6. Martin said on November 13, 2017 at 2:16 pm

    The solution for me was different. I had a freeze non stop after opening. You click on icon of Thunderbird, right click, properties, comp. , run as administrator checkbox. And all issues gone

  7. CJ Macneal said on November 24, 2016 at 5:38 pm

    On TB version 45.5 there is a .msf repair tool under (top menu bar) Edit – Folder Properties. Worked! Thanks so much for the .msf tip. Seems to have been my problem.

  8. Jeffry Houser said on March 7, 2016 at 1:56 pm

    For the record, the solution to my problem on Windows 10 had nothing to do w/ .msf files.

    Bring up tools –> Options –> Advanced –> General

    Unclick “Allow Windows to search messages”

    Boom, no more hanging mail client.

    1. Kenny Danielson said on May 2, 2016 at 3:42 pm

      That fixed it for me – at least for now. Time will tell.

      Thanks Jeffry!

  9. guts said on March 6, 2016 at 10:53 pm


    I love thunderbird and because of this problem, i was considering uninstalling it.

    You save me.

    Thanks (again :) )

  10. Eric Buist said on December 22, 2015 at 2:48 pm

    Good attempt, but I cannot find any msf file in my Thunderbird profile. The format probably changed or I would have to search in all files/all directories, which is hard on Windows where the problem happens. I don’t have this issue on Ubuntu, where I could use find to search for msf files in all the filesystem. I cannot spend my time installing new and new software tools (Thunderfix, a find utility, etc.), because now, it takes forever to find the Download links on overcrowded pages, and Windows programs now often install spyware which cause issues after. Unfortunately, there is no apt-get-like package manager on Windows that could at least help with the find-download-link process.

    1. Jeffry Houser said on February 3, 2016 at 7:13 pm

      I’m not sure why you would say that searching in all files / all directories is hard on Windows.

      On my Windows 10 machine; I opened up my profile:

      “C:\Users\{my login name}\AppData\Roaming\Thunderbird\Profiles\{some weird string of characters}.default”

      then I typed *.msf in the top right corner [the search box] and it brought up 150+ .msf files. I selected and deleted all of them. That appears to have solved my issue for the moment.

      I spent more time Googling for a solution than I did following the above steps.

  11. Milton Akridge said on October 11, 2015 at 12:37 am

    NOTE: These fixes were not authored by me, but fixed an intermittent freezing problem I had with Thunderbird mail client:

    “T-bird freeze:
    After installing Windows 10, I had the issue with the Runtime Broker taking ~30% of my CPU. I found the fix (at least for me) by going to Settings -> System -> Notifications & actions and unselecting “Show me tips about Windows.” It immediately fixed the processor usage when I disabled it, and immediately came back when I re-enabled it. I couldn’t find this anywhere, so I thought it could help a couple people if I posted it somewhere, at least.
    I recorded the weirdness here:
    My save was updating both ethernet driver and bios”

    Go to Account Settings > Server Settings > :toggle check marks on each setting—— each box. (Don’t know why, but this simple procedure fixes the random freezing on the T-bird email client!)”

  12. Martin Lefkowitz said on February 7, 2015 at 8:44 pm

    Thunderfix just wiped out all my emails, filters, and configuration. While it did say “do this at your own risk, I didn’t expect to loose everything. Bad program.

    1. Martin Brinkmann said on February 7, 2015 at 8:53 pm

      I’m sorry to hear that. Did you create a backup of your profile beforehand?

      1. Dave Costain said on March 11, 2018 at 10:51 pm

        I have a frozen Thunderbird which does not let me back-up, so I can’t yet use Thunderfix for fear of losing all my e-mails as per the previous poster. I hope to find your answer by reading subsequent posts after leaving this reply.

  13. Jörg Wagner said on October 4, 2012 at 9:08 pm

    Great tip!
    I have struggled with Thunderbird’s lags for almost a year – on a lightning fast machine with SSD hard disk. With your info I could finally solve the problem within minutes. I used “Search Everything” on Windows to locate all .msf files, made sure they were all within Thunderbird profile folders, and deleted them altogether. After starting TB it took some time after my large IMAP and local folders were rebuilt, but it went smoothly and now my system is back to normal.
    It has literally cost me hours each month that I spent waiting for the busy-spinner to disappear and TB to return to duty.
    Many thanks again!!!

  14. rakotomandimby said on June 1, 2012 at 3:24 pm

    To fire all my MSF files, I used
    $ find . -type f -name ‘*.msf’ -exec rm {} ;

    Indeed, I noticed the MSF files had old (1month earlier) timestamps: Having such old index files is obviously leading to performance problems.

    My ImapMail folder is 5.3G big, with mostly test and HTML messages (I receive only a few messages with huge attachments). Malformed index on such quantity is PITA…

  15. klairev said on November 7, 2011 at 5:28 pm

    You ROCK. Thank you so much for taking the time to post this. My Thunderbird was so slow it was unbearable, I did what you said, and now it’s perfect! Thanks!!!

  16. Derrick W. said on March 8, 2010 at 7:55 pm

    I am looking for a solution to Mozzila Thunderbired email program taking a long time to open folders or move messages to folders can i delete the .msf for the indevidule folders to speed them up

    1. Kelly said on September 14, 2010 at 5:51 am


      In fact, download ThunderFix and it will detect and delete all your .msf files. Works great.

      1. Derek said on May 7, 2017 at 4:56 pm


  17. Ben said on July 2, 2009 at 3:54 am

    If you only experience slowness reading HTML emails with Thunderbird 2.0x, then it might be this bug:

    Thunderbird Freeze and high CPU Utilization when loading HTML messages

    The workaround is to leave the address book open to make the HTML emails open fast.

    Ben in Chevy Chase, MD

  18. BalaC said on May 20, 2009 at 5:34 pm

    Martin, i think you forgot to include link to download this stuff.

    1. Martin said on May 20, 2009 at 7:10 pm

      thanks, added.

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