Mozilla Thunderbird is a fast and very functional GUI mail client. It features excellent online/offline mail reading, IMAP, POP and local mail transfer protocols, security with X.509 and GPG key management, and a plethora of extensions.
Thunderbird follows in the tradition of Mozilla Firefox. It is a focused, lightweight mail client with very good extensibility through the Mozilla extension mechanism.
Thunderbird is widely localised and available in many languages.
3.3 series is the current focus of development.
Mozilla Thunderbird does not have any download files registered with Launchpad.