If you've ever used Mozilla Firefox, you will probably find that Thunderbird’s interface is very similar. It has convenient tabs to separate its different functions the same way you use them to browse several web pages at the same time. Moreover, those who have been using Microsoft Outlook for a while are likely to use Thunderbird without much trouble because both applications have very similar ways to handle email messages. The use of different sets of email folders comes in very handy when you are using various mail accounts. Thus, your personal messages will never muddle up with your business mail. Searching an email is also very convenient as, there are 2 search bars, one on the top is for searching the email from all the accounts within the Thunderbird and the 2nd bar can be used to search for something in a particular account. Searches can be saved to virtual folders that automatically aggregate relevant mail in Thunderbird. Thunderbird incorporates a Bayesian spam filter, a whitelist based on the included address book, and can also understand classifications by server-based filters such as SpamAssassin.
Mozilla Thunderbird offers rich HTML formatting conscious of your computer's security and your privacy. S/MIME support lets you encrypt and sign mail in Mozilla Thunderbird (with an OpenPGP plug-in available as well). In addition to sending files as direct attachments, Mozilla Thunderbird can automatically upload them to a file sending service and keep the email messages themselves small. You can run Mozilla Thunderbird from a removable medium such as a USB stick. Many extensions more allow Mozilla Thunderbird to expand its feature set or improve usability. Extensions allow the addition of features through the installation of XPInstall modules (known as "XPI" or "zippy" installation) via the add-ons website that also features an update functionality to update the extensions. An example of a popular extension is Lightning, which adds calendar functionality to Thunderbird. Thunderbird supports a variety of themes for changing its overall look and feel. These packages of CSS and image files can be downloaded via the add-ons website at Mozilla.