You can reply to emails using Mozilla Thunderbird instead of using cPanel Webmail.
1. Open Mozilla Thunderbird.
2. Click on the email you wish to open twice.
3. In the top area on right side, click on the "Reply" button. Or "Reply All" if you want to reply to everyone who was in the To and Cc box of the message you received... but use Reply All wisely!
4. Type your message in a message box and click "Send".