Thunderbird is a simple to use, powerful, full-featured, and customizable 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.
Pros: Thunderbird is easily expandable and has a large and fast-growing user base (mostly Outlook Express refugees). Thunderbird is a cross-platform email application for Mac, Windows, and Linux.
Cons: None significant.