Thunderbird is an open source, cross-platform email, news, and chat client developed by the Mozilla Foundation.
1. Thunderbird can manage multiple email, newsgroup, and news feed accounts and supports multiple identities within accounts.
2. Features such as quick search, saved search folders, advanced message filtering, message grouping, and labels help manage and find messages.
3. Thunderbird provides enterprise and government-grade security features such as SSL/TLS connections to IMAP and SMTP servers.
4. It also offers native support for S/MIME secure email (digital signing and message encryption using certificates).