Steps to save copies of your emails on your computer as EML files

Step 1. Launch Thunderbird.
Step 2. Select the desired email folder (e.g. Inbox).
Step 3. Select the email you want to export. Or press CTRL+A to select all emails.
Step 4. Click the menu button to display the Thunderbird menu.
Step 5. Select Save as > File …
Step 6. Navigate to the desired destination folder and click Select Folder.
The selected emails are now exported to the target folder. The EML files created in this way can be opened with many email programs.
Step 7. Repeat the steps for each folder you want to back up.