With Thunderbird open, click on the “Tools” menu, then click on “Account Settings”.
Select “Add Mail Account” under Account Actions
Enter the name you want displayed when you send email in the “Your Name” field, and the POP email address you created for your WebMail account in the “Email Address” field. Click Continue
Make sure that “POP” is selected. Enter “mail.yourdomain.com” in the “Incoming Server” field. If this is the first email account you are setting up in Thunderbird, you will also be asked for an Outgoing Server. Enter “mail.yourdomain.com” as the Outgoing Server as well. Click “Next”.
Enter your full POP email address (firstname.lastname@example.org) in the “User Name” field. Click “Next”.
Enter a name for this account in the “Account Name” field. Click “Next”.