Do you have only a local version of your emails or have they been previously downloaded? You can easily upload them to GoldFynch. Learn how to do so 

Step 1. Launch Thunderbird

Step 2. Select the folder that you want to export the emails from

Step 3. Select all emails in the folder by pressing Ctrl+A. Or, select the specific emails that you want to export

Step 4. Click the menu button to display the Thunderbird menu

Step 5. Select Save as> File 

Step 6. Select the folder where the emails should be saved 

Step 7. Click Save

Once the mbox is created you can upload it to GoldFynch