How to Keep Thunderbird Email Running Smoothly

If your Mozilla Thunderbird email client is running slowly, especially when deleting messages, it might be overloaded or in need of maintenance. A few simple steps can significantly speed things up and prevent future slowdowns. Here are instructions on how to keep Thunderbird in top shape, from daily cleaning to more advanced troubleshooting. These instructions are based on Thunderbird for Windows, version 140.4.0esr, released on October 14, 2025.

1. Keep Your Folders Tidy

The single biggest cause of a slow Thunderbird is too many messages in key folders.

Keep Folder Sizes Manageable

Your Inbox is the first folder Thunderbird loads. If it contains tens of thousands of messages, the program will struggle. The same applies to any folder that you frequently access.

• Recommendation: Avoid keeping more than a few thousand messages in your Inbox.
• Solution: Regularly move old emails you want to keep into an “Archive” folder or other subfolders. The goal is to keep the main Inbox folder as light as possible.

How to Clean Faster (Selecting Multiple Messages)

To clean your Inbox quickly, you need to select many messages at once. Here’s how:

• To select a continuous block of messages:
  
  1. Click on the first message in the group.
  
  2. Hold down the SHIFT key on your keyboard.
  
  3. While still holding SHIFT, click the last message in the group.
  
  (This will select both messages you clicked and everything in between.)
• To select several separate messages:
  
  1. Click on one message you want to select.
  
  2. Hold down the CTRL key (or Cmd ⌘ on a Mac).
  
  3. While still holding CTRL, click on each of the other messages you want.
• To select ALL messages in a folder:
  
  1. Click anywhere in the message list.
  
  2. Hold down the CTRL key (or Cmd ⌘ on a Mac).
  
  3. While still holding it, press the A key.

After you’ve selected your messages, you can press the Delete key, press the A key to Archive them, or right-click to choose “Move To”.

Empty the Trash Folder (Very Important!)

When you delete a message, it just moves to the Trash. Like your Inbox, if the Trash gets too full (sometimes with tens of thousands of messages), it can slow down the entire program. Empty it regularly.

1. Find your Trash folder in the folder list on the left.
2. Right-click on the word “Trash”.
3. From the menu that appears, select “Empty Trash”.
4. It might ask you to confirm. Click “OK”.

2. Compact Your Folders

This is a crucial maintenance step. When you delete a message or move it, Thunderbird doesn’t truly remove it right away; it just “hides” it. Compacting a folder is the process that permanently purges the hidden data and reclaims the space. After a big cleanup (like emptying the trash), compacting is essential for performance.

1. Right-click on any folder you’ve changed (like your Inbox or Trash).
2. Select “Compact” from the menu.
3. You can also set Thunderbird to do this automatically.

For more details, see the official support guide: Compacting folders in Thunderbird.

3. Manage Open Email Tabs

Having too many tabs open can consume your computer’s resources and slow Thunderbird down.

How to close tabs:

• Close one tab: Click the small ‘X’ on the tab itself.
• Close many tabs at once: Right-click on any tab and choose “Close Other Tabs”.

How to prevent tabs from building up:

A better way to manage this is to change a setting so emails open in their own window, not a new tab.

1. Click the menu button (three horizontal lines ☰) in the top-right corner.
2. Go to Settings (or Options).
3. Select General from the list on the left.
4. Scroll down to the Reading & Display section.
5. Find the “Open messages in:” setting and change it from “A new tab” to “A new message window” or “An existing message window”.
6. You can close the settings tab; your change is saved automatically.

In that same section, you might also find it helpful to check the box for “Close message window/tab on move or delete”.

4. Check for Thunderbird Updates

Software updates often include important performance improvements and security fixes. Running an old version can sometimes be the cause of slowdowns.

1. Click the menu button (three horizontal lines ☰) in the top-right corner.
2. Go to Help, then select About Thunderbird.
3. A new window will open and automatically check for updates. If one is found, it will be downloaded and installed.

For more information, see the support page: Updating Thunderbird.

5. Rebuild the Global Search Database (Advanced)

If searching is slow or general performance is poor, Thunderbird’s “Global Search” database might be corrupted or bloated. Rebuilding it can solve these issues.

This is a more advanced step that involves either disabling the search feature or manually deleting a database file from your Thunderbird profile. Because this process is more technical, we recommend following the official guide precisely.

See the official instructions here: Rebuilding the Global Database.

Need More Help?

For any other questions or for more detailed guides, the official Mozilla Thunderbird support website is an excellent resource:

https://support.mozilla.org/en-US/products/thunderbird