Mozilla Thunderbird is a cross-platform, open source e-mail client that competes with the likes of Microsoft Outlook and Eudora Mail. Mozilla Thunderbird originated as an offshoot of the Mozilla Firefox Web browser project and was developed by the same team until Mozilla Corporation released development to an independent organization in order to focus efforts on Firefox.
Like Mozilla Firefox, Thunderbird supports add-ons, extensions that provide additional functionality to the e-mail client. One of the key extensions available for Mozilla Thunderbird is Mozilla Lightning, an extension that adds calendar and personal information manager (PIM) capabilities to Thunderbird.
