Mozilla Thunderbird provides users with option of requesting return receipts when sending messages. This feature can be enabled using the Thunderbird Options menu.
Click Tools menu, and select Options from the list of available menus.
This would display the following Options dialog window.
Navigate to Advanced tab and click the Return Receipts button to launch the Return Receipts window.
Mark the check box with label as When sending messages, always request a return receipts. This would enable the return receipts feature in Mozilla Thunderbird. Click Ok button to confirm and save the changes.