What to do if Thunderbird is slow on Windows 10

Milan Stanojevic
by Milan Stanojevic
Deputy Editor
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Thunderbird slow

Thunderbird is a popular email client and many Windows 10 users utilize it. Despite its popularity and simplicity, some users reported that Thunderbird is slow on Windows 10, so let’s see if we can fix that problem.

What can I do if Thunderbird is slow to send emails?

1. Start Windows 10 in Safe Mode

According to users, sometimes third-party applications and your settings can interfere with Thunderbird and cause it to become slow.

In order to check if third-party applications are the problem, you can try running Thunderbird from Windows 10 Safe Mode. To enter Safe Mode, you need to do the following:

  1. Open the Start Menu and click the Power button.
  2. Hold Shift key and choose Restart option.
    thunderbird-slow-restart-1
  3. Your PC will now restart and you’ll see three options on the screen. Select Troubleshoot.
  4. Now choose Advanced options > Startup Settings.
  5. Click the Restart button.
  6. When your PC restarts you’ll see a list of options available.
  7. Select Safe Mode with Networking by pressing F5 on your keyboard.

After Safe Mode starts you need to locate and run Thunderbird. If Thunderbird works without any problems, it means that the issue is caused by a third-party application or by your configuration settings.

Solution 2 – Start Thunderbird in Safe Mode

Just like Windows, Thunderbird also has its own Safe Mode, and by using Safe Mode you’ll reset Thunderbird to default settings. In addition to resetting Thunderbird, you’ll also temporarily disable all third-party extensions that might be interfering with Thunderbird.

To start Thunderbird in Safe Mode, you need to do the following:

  1. Hold the Shift key on your keyboard and start Thunderbird.
  2. Thunderbird Safe Mode window will now appear. If you want, you can choose the option to Disable all add-ons or to Reset toolbars and controls.
  3. Click Continue in Safe Mode button to start Thunderbird in Safe Mode.

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You can also access Safe Mode while in Thunderbird simply by clicking the Help menu and choosing the Restart with Add-ons Disabled option. After that just click Restart button and Thunderbird will start again in Safe Mode.

Once Thunderbird starts in Safe Mode, check if everything is in order. If there are no problems, it means that your Thunderbird configuration or one of installed add-ons is causing this issue, so be sure to change your settings and disable unnecessary add-ons.

Some users are also suggesting to start Thunderbird Safe Mode while you’re in Windows 10 Safe Mode, so be sure to try that as well.

3. Change your email client

This might seem like a drastic solution, but it’s actually a practical move.

If you simply do not want to deal with the hassle of a troubleshooting process, switching email clients is the logical step and we have a powerful recommendation for you.

Install Mailbird

If Thunderbird is slow to send emails or download attachments, this non-lagging software will feel like a breeze.

Mailbird is a top-rated email client, designed to complement the Windows 10 structure to the point where it seamlessly blends with the OS’s architecture.

This email client features an uncluttered and very intuitive interface that will allow you to easily manage your emails, attachments, and contacts in one unified Inbox.

Speaking about that, the incredible Attachment Search feature allows you to quickly and effortlessly track down even year-old attachments.

By adding integrations to the table (and Mailbird surely does allow you to connect all your favorite email, calendar, task, and messaging apps into one), you will enjoy a plethora of functionalities to cover all your communication needs.

Let’s quickly look at its key features:

  • Easy emails and contacts management  from a unified Inbox
  • Customization options (numerous free color themes, different Windows-adapted layouts and more)
  • Seamless app integrations (Facebook, Twitter, Whatsapp, Dropbox, Google Calendar, Asana and more)
  • Snooze feature to separate and prioritize your emails
  • Custom Sounds notifications for incoming and outgoing emails
  • Intuitive keyboard shortcuts for archiving, composing, replying, and forwarding
  • Multi-language 24/7 free support
Mailbird

Mailbird

Why settle for an unresponsive email app? Get more options, ease of use, and quick actions from the snappy Mailbird!

4. Keep your Thunderbird up to date

If your Thunderbird is slow on Windows 10, be sure that you have the latest updates installed.

The community is working hard on Thunderbird, and if you’re having certain issues with it on Windows 10, we strongly advise that you check if you have the latest version installed.

Some versions of Thunderbird might suffer from certain issues, and in order to fix those issues, it’s highly recommended that you download and install the latest version.

After installing the latest version of Thunderbird on your PC, check if the issue is resolved.

5. Delete the msf files

Thunderbird uses MSF files to store the index of all emails, but sometimes these files can get corrupted, and that can cause Thunderbird to become slow. In order to fix this problem, you need to delete MSF files from the Thunderbird folder.

Keep in mind that MSF files will be recreated as soon as you start Thunderbird, so none of your emails will be deleted. To delete MSF files, do the following:

  1. Make sure that Thunderbird is completely closed.
  2. Press Windows Key + R and enter %appdata%. Click OK or press Enter.
    thunderbird-slow-appdata-1
  3. Go to the ThunderbirdProfiles folder and open your profile directory.
  4. If you use IMAP account navigate to ImapMail folder. If you use a POP account, choose Mail/Local Folders.
  5. Now locate the MSF files and remove them. Be sure to only remove MSF files from that folder.
  6. After deleting these files start Thunderbird again and check if the problem is resolved.

Leave no Thunderbird issue unsolved. Take a look at this amazing troubleshooting guide.


If deleting MSF files manually seems complicated to you, some users are recommending to use the ThunderFix tool, so you might want to try it.

With this tool, you just need to select your profile and click the Fix profile button and all msf files will be removed.

6. Use Config Editor

Some versions of Thunderbird use Direct2D hardware acceleration, and this feature can sometimes reduce your performance, especially if you’re using a low-end graphic processor on your PC.

You can disable this feature by using Config Editor in Thunderbird. To do that, follow these steps:

  1. Go to Settings > Options > Config Editor.
  2. When Config Editor opens, set gfx.direct2d.disabled to true and layers.acceleration.disabled to true.
  3. Save changes and the problem should be completely resolved.

Few users reported that they fixed the problem simply by using layers.acceleration.disabled option, so you might want to try doing that.

7. Turn on Automatic Compacting of Folders

You can improve the performance of Thunderbird simply by turning on the Automatic Compacting feature. To do that, follow these steps:

  1. Go to Tools > Options.
  2. Navigate to the Advanced tab and select Network & Disk Space.
  3. Select Compact folders when it will save over option and enter the desired size in MB. 20MB is usually a good option, but you can use a lower value if you want compacting to be performed more frequently.

If you decide to use a lower value for Automatic Compacting, be sure to set mail.purge.ask to true using Config Editor in Thunderbird.

Another way to improve performance in Thunderbird is to disable Global Search and Indexer feature. This feature is useful if you search for your emails using keywords, but if you’re a basic user you probably aren’t using this feature.

To disable Global Search, do the following:

  1. Go to Tools > Options.
  2. Now go to Advanced tab > General.
  3. Under the Advanced Configuration section disable Enable Global Search and Indexer.

You can also improve the performance of Thunderbird simply by disabling the Message Pane feature.

To do that, navigate to View > Layout and disable the Message Pane option. Some users claim that they fixed the problem with slow Thunderbird simply by turning on Fetch headers online option in the Server Settings window, so you might want to try that.

8. Add Thunderbird to the list of exclusions

Certain antivirus tools keep a close eye on your email client and scan all your emails. This is a great feature since it scans all your emails for malicious attachments, but despite its usefulness sometimes you can experience performance issues with Thunderbird.

If your Thunderbird is slow, be sure to add it to the list of exclusions in your antivirus software and check if that fixes the problem.

Keep in mind that adding Thunderbird to the list of exclusions can be a security risk sometimes, so be sure not to open any suspicious emails or attachments.

If that doesn’t fix the problem, you might want to consider disabling your antivirus software temporarily and checking if that solves the issue.

If the issue is resolved by disabling your antivirus, be sure to switch to a different antivirus software and check if the issue persists.


Check out these best antivirus solutions to match your Windows 10 PC for maximum protection.


9. Make your messages available offline

Users reported that Thunderbird is slow to load messages on Windows 10, and if you have this problem on your PC, you might want to make your messages available offline. To do that, follow these steps:

  1. Go to Tools > Account Settings.
  2. Now go to your IMAP Account Settings and look for Offline & Disk Space section.
  3. Check Make the messages in my Inbox available when I am working offline.

By enabling this option all your messages will be downloaded to your hard drive, and you’ll be able to open them instantly while having all advantages of IMAP account. If you want, you can also make other folders available offline.

10. Change Maximum number of server connections

According to users, you might be able to fix the problem with Thunderbird simply by changing the Maximum number of server connections value. To do that, follow these steps:

  1. Go to Account Settings > Server Settings > Advanced.
  2. Locate Maximum number of server connections to cache and change it to 1.

Apparently the issue is caused if the number of connections is higher than 1. If this value is higher than 1, Thunderbird tries to connect multiple times to the server.

After the server rejects all these connections the entire process might slow down, therefore be sure to change Maximum number of server connections to 1.

11. Keep your folders small

According to users, if you have more than 1000 email messages in a folder that can lead to some issues on your PC. To fix this problem, be sure that you frequently delete contents from the Trash folder.

If you want to keep your folders small, you can permanently delete an email simply by holding the Shift key and choosing the delete option.


Having performance issues with Thunderbird can be a big problem, but we hope that you managed to fix the problem by using one of our solutions.

Feel free to share your troubleshooting experience with us in the comments section below.

Editor’s Note: This post was originally published in November 2016 and has been since revamped and updated in July 2020 for freshness, accuracy, and comprehensiveness.