To configure your email account in Thunderbird, follow the steps below
Start Thunderbird, go to the File menu and click New -> Account
In the Account Wizard dialog box, select Email account and then click Next
Enter your name as you would like it to appear for any mail that you send, and your complete email address (firstname.lastname@example.org)
Select the type of incoming server you are using as either POP / IMAP.
Login to your Webmail account. To access your Webmail interface, you can use the URL of the form http://webmail.yourdomainname.com. Here, you would need to login with your email address and the corresponding password. Go to Settings >> Forwarding and POP / IMAP Settings to obtain the corresponding incoming server name. Enter the Incoming Mail Server name and the Outgoing Server name in the corresponding boxes and click Next.
Enter your full email address as the Incoming User Name and your Outgoing User Name and click Next
In the Account Name box, you can enter any name that would help you identify this mailbox and click Next.
Verify your account information and click Finish.
Thats it, your account has been setup! When you click on Get Mail, all your email will be downloaded by Thunderbird.