Mozilla Lightning brings the Sunbird calendar to the popular email client, Mozilla Thunderbird. Since it's an extension, Lightning is tightly integrated with Thunderbird, allowing it to easily perform email-related calendaring tasks.
Lightning is licensed under the MPL/GPL/LGPL triple license, allowing use of the files under the terms of any one of the Mozilla Public License, the GNU General Public License, or the GNU Lesser General Public License.

The license of this software is Freeware, you can free download and free use this bulk email software.