You need to follow the below steps correctly to-do-so: Launch the Yahoo backup software and log in with your details. Select the folders from the tree you want to import and click Next. Select Thunderbird from the option to save the backup file. Check the Mail filter to import emails between a specific date range. Choose the path of the folder to save Yahoo emails. Choose the other options as per need. Click on the Convert button to start the importing process. Download the report of migration if required.