Thunderbird is an email, newsgroup, news feed and chat (XMPP, IRC, Twitter) client. The vanilla version is not a personal information manager, although the Mozilla Lightning extension adds PIM functionality. Additional features, if needed, are often available via other extensions.
Message management
Thunderbird can manage multiple email, newsgroup and news feed accounts and supports multiple identities within accounts. Features like quick search, saved search folders ("virtual folders"), advanced message filtering, message grouping, and labels help manage and find messages. On Linux-based systems, system mail (movemail) accounts are supported. A still unsolved problem regards the possibility to archive email messages on disk. When exporting a message, by saving or dragging and dropping, the timestamp of the exported file given by Thunderbird is that of the moment in which the file was exported. For archiving reasons it would be necessary that exported file had the timestamp corresponding to the moment in which it was sent or received.
Junk filtering
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.
Extensions and themes
Extensions allow the addition of features through the installation of XPInstall modules (known as "XPI" or "zippy" installation) via the add-ons website which 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 Add-ons.
Standards support
Thunderbird supports POP and IMAP. It also supports LDAP address completion. The built-in RSS/Atom reader can also be used as a simple news aggregator. Thunderbird supports the S/MIME standard, extensions such as Enigmail and support for the OpenPGP standard.
List of supported IMAP extensions: https://wiki.mozilla.org/MailNews:Supported_IMAP_extensions
File formats supported
mbox – Unix mailbox format
Mork – used for internal database
SQLite – also used for internal database (since version 3)
Cross-platform support
Thunderbird runs on a wide variety of platforms. Releases available on the primary distribution site support the following operating systems:
Windows
Linux
OS X
OpenSolaris
FreeBSD
OS/2 and eComStation
The source code is freely available and can be compiled to be run on a variety of other architectures and operating systems.
Internationalization and localization
Thunderbird does not yet support SMTPUTF8 (RFC 6531) or Email Address Internationalization.
With contributors all over the world, the client is translated into at least 52 languages, but client's addresses are currently limited to ASCII local parts.
32/64-bit support
Operating System
32-bit support
64-bit support
Windows
Yes
No
OS X
Yes
Yes
Linux
Yes
Yes
Security
Thunderbird provides enterprise and government-grade security features such as SSL/TLS connections to IMAP and SMTP servers. It also offers native support for S/MIME secure email (digital signing and message encryption using certificates). Any of these security features can take advantage of smartcards with the installation of additional extensions.
Other security features can be added through extensions. For instance, Enigmail offers PGP signing, encryption, and decryption.
Optional security protections also include disabling loading of remote images within messages, enabling only specific media types (sanitizer), and disabling JavaScript.
The French military uses Thunderbird and contributes to its security features, which are claimed to match the requirements for NATO's closed messaging system.
