Thunderbird is an Open Source Desktop Email Client developed by Mozilla Foundation. It is well known for its Themes and Addons developed by huge community of Open Source Developers.
When users are tired of using Microsoft Outlook and are in search of Alternative Desktop Email Client, they choose Thunderbird. Apart from receiving and sending mails users can do whole lot of work like create Folders, Filters, Apply Themes and use Thunderbird Addons to make work easier.