This easy step-by-step guide will help you set up Thunderbird to sync your Calendar items.
Before you begin, you must download and install Lightning by Mozilla. You can download it here: https://www.mozilla.org/en-US/projects/calendar/
Once you have downloaded and saved it to your hard drive, you must open Thunderbird, then open Add-ons from the Tools menu. From the options button next to the Search all add-ons field, select Install Add-on From File... and locate the downloaded add-on. Once you've installed Lightning, you are ready to sync your Calendar with CalDAV.
Step 1. Login to your webmail with your full firstname.lastname@example.org email address in the Username field and your Password
Step 2. To sync your Calendar items, click on Calendar in the App Launcher
Step 3. Click the down arrow next to the calendar you wish to sync and select Share Calendar
Step 4. Right click on the Mozilla Thunderbird link at the bottom of the popup window, and click Copy link address
Step 5. Open Thunderbird
Click the File menu (top left)
Click Account Settings, and the Account Settings... dialog box will appear
Click Account Settings within the dialog box
Step 6. The Account Settings window will open
Click on the Internet Calendars tab
Paste the website address copied in step 4
Congratulations, you have synced your Calendar in Outlook 2010!