Thunderbird

Simple to use, powerful, and customizable, Thunderbird is a full-featured email application. Thunderbird supports IMAP and POP mail protocols, as well as HTML mail formatting. Easily import your existing email accounts and messages. Built-in RSS capabilities, powerful quick search, spell check as you type, global inbox, deleting attachments and advanced message filtering round out Thunderbird's modern feature set.

Thunderbird features advanced security protocols such as anti-phishing, spam filters and provides enterprise and government grade security features including S/MIME, digital signing, message encryption, support for certificates and security devices. Attachments are never run without your express permission, protecting you from many worms and viruses.