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Mozilla Thunderbird

Mozilla Thunderbird
Mozilla Thunderbird 17.0 on Ubuntu
Developer(s) Mozilla Foundation (formerly Mozilla Messaging)
Initial release July 28, 2003 (2003-07-28)
Stable release 38.3.0 (September 29, 2015 (2015-09-29)[1])
Preview release 42.0 Beta 2 (October 13, 2015 (2015-10-13)[2][3])
Written in C, C++, JavaScript,[4] CSS,[5][6] XUL, XBL
Operating system Windows XP SP2 or later; OS X 10.6 or later; Linux[7]
Size 25 MiB
Available in 53 languages
Type Email client, news client, feed reader
License MPL[9]
Website /thunderbird.orgmozilla

Mozilla Thunderbird is a free,[10] open source, cross-platform email, news, and chat client developed by the Mozilla Foundation. The project strategy was modeled after that of the Mozilla Firefox web browser.

On December 7, 2004, version 1.0 was released, and received more than 500,000 downloads in its first three days of release, and 1,000,000 in 10 days.[11][12]

On July 6, 2012, Mozilla announced the company was dropping the priority of Thunderbird development because the continuous effort to extend Thunderbird's feature set was mostly fruitless. The new development model is based on Mozilla offering only "Extended Support Releases", which deliver security and maintenance updates, while allowing the community to take over the development of new features.[13][14]

On November 25, 2014, Kent James of the volunteer-led Thunderbird Council announced that more staff are required to be working full-time on Thunderbird so that, through the Council, there can be stable and reliable product releases, and progress made on features that have been frequently requested by the community.[15]


  • Features 1
    • Message management 1.1
    • Junk filtering 1.2
    • Extensions and themes 1.3
    • Standards support 1.4
    • File formats supported 1.5
    • Limits and known issues 1.6
    • Cross-platform support 1.7
    • Internationalization and localization 1.8
    • Security 1.9
  • History 2
    • Releases 2.1
  • References 3
  • External links 4


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 such as 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.

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.[16]

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 that 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.[17]

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 add support for the OpenPGP standard.

List of supported IMAP extensions at[18]

File formats supported

Thunderbird provides mailbox format support using plugins, but this feature is not yet enabled due to related work in progress.[19] The mailbox formats supported as of July 2014 are:

  • mbox – Unix mailbox format (one file holding many emails)
  • maildir – known as maildir-lite (one file per email). Note: not yet stable, as of July 2014 Mozilla advise this format is still "too buggy for normal use"[20]

Thunderbird also uses Mork and (since version 3) MozStorage (which is based on SQLite) for its internal database. Mork was due to be replaced with MozStorage in Thunderbird 3.0.,[21] but the 8.0 release still uses the Mork file format. The current version of SeaMonkey, version 2.14.1, also still uses Mork for its indexes for both POP and IMAP mail folders (at least).

Limits and known issues

The default mailbox format ("mbox") back-end allows a mailbox up to very large sizes (64 bit or file system limit). However, if used in Local Folder mode, as is the case for POP3 email storage and other offline email stores, it has a usable limit of 4GB, with data corruption possible if this size is exceeded,[20] although Thunderbird tries to detect and prevent this. The limit was being actively worked on[22] by developers in 2013 and remains open; it does not affect IMAP mail storage.[20] Compaction of near-4GB mailboxes is also potentially "very slow".[20]

An issue also exists related to overly-long filenames in some cases, since Thunderbird must rely on the local computer for filing system limitations, while external email (IMAP especially) can have nested email folders with arbitrary length paths and filenames that cannot be stored under their intended paths and names.[20]

Cross-platform support

Thunderbird runs on a variety of platforms. Releases available on the primary distribution site support the following operating systems:[23][24]

Unofficial ports are available for:

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

With contributors all over the world, the client is translated into more than 50 languages, although email addresses are currently limited to ASCII local parts.[29] Thunderbird does not yet support SMTPUTF8 (RFC 6531) or Email Address Internationalization.


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 may 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.[30]


Originally launched as Minotaur shortly after Phoenix (the original name for Mozilla Firefox), the project failed to gain momentum. With the success of the latter, however, demand increased for a mail client to go with it, and the work on Minotaur was revived under the new name of Thunderbird, and migrated to the new toolkit developed by the Firefox team.

Significant work on Thunderbird restarted with the announcement that from version 1.5 onward, the main Mozilla suite would be designed around separate applications using this new toolkit. This contrasts with the previous all-in-one approach, allowing users to mix and match the Mozilla applications with alternatives. The original Mozilla Suite continues to be developed as SeaMonkey.

On December 23, 2004, Project Lightning was announced which tightly integrated calendar functionality (scheduling, tasks, etc.) into Thunderbird, and which is now available as a downloadable extension.

On October 11, 2006, Qualcomm and the Mozilla Foundation announced that "future versions of Eudora will be based upon the same technology platform as the open source Mozilla Thunderbird email program."[31] The project is code-named Penelope.

In late 2006, Debian rebranded Thunderbird as Icedove due to trademark and copyright reasons. This was the second product to be rebranded.[10][32]

On July 26, 2007, the Mozilla Foundation announced that Thunderbird would be developed by an independent organization, because the Mozilla Corporation (a subsidiary of the foundation) was focusing on Mozilla Firefox development.[33]

On September 17, 2007, the Mozilla Foundation announced the funding of a new internet communications initiative with Dr. David Ascher of ActiveState. The purpose of this initiative was "to develop Internet communications software based on the Thunderbird product, code, and brand".[34]

On February 19, 2008, Mozilla Messaging started operations as a subsidiary of the Mozilla Foundation responsible for the development of email and similar communications. Its initial focus was on the then upcoming version of Thunderbird 3. Alpha Preview releases of Thunderbird 3 were codenamed "Shredder".

On April 4, 2011, Mozilla Messaging was merged into the Mozilla Labs group of the Mozilla Foundation.[35]

On July 6, 2012, a confidential memo from Jb Piacentino, the Thunderbird Managing Director at Mozilla, was leaked and published to TechCrunch.[36] The memo indicated that Mozilla would be moving some of the team off the project and further development of new features would be left up to the community. The memo was slated for release on July 9, 2012. A subsequent article by the Mozilla Foundation Chair, Mitchell Baker, stated Mozilla's decision to make a transition of Thunderbird to a new release and governance model.[13][14]

On November 25, 2014, Kent James of the volunteer-led Thunderbird Council announced on the Thunderbird blog that active contributors to Thunderbird gathered at the Mozilla office in Toronto and discussed the future of the application. They have decided that more staff are required working full-time on Thunderbird so that the Thunderbird Team can release a stable and reliable product and make progress on features that have been frequently requested by the community.


Thunderbird development releases occur in three stages, called Beta, Earlybird, and Daily, which correspond to Firefox's Beta, Aurora, and Nightly stages. The release dates and Gecko versions are exactly the same as Firefox; for example, Firefox 7 and Thunderbird 7 were both released on September 27, 2011, and were both based on Gecko 7.0.


  1. ^ "Thunderbird — Notes (38.3.0) — Mozilla".  
  2. ^ "Thunderbird — Beta Notes (42.0beta) — Mozilla". 2015-10-13. Retrieved 2015-10-14. 
  3. ^ "Mozilla Thunderbird - Help us test the latest beta". Retrieved 2015-10-14. 
  4. ^ "Firefox's addons are written in JavaScript". Rietta. Retrieved December 19, 2009. 
  5. ^ "Firefox uses an "html.css" stylesheet for default rendering styles". David Walsh. Retrieved December 19, 2009. 
  6. ^ "The Firefox addon, Stylish takes advantage of Firefox's CSS rendering to change the appearance of Firefox". Archived from the original on May 23, 2009. Retrieved December 19, 2009. 
  7. ^ "Thunderbird 31.0 System Requirements". Mozilla Messaging. Retrieved November 18, 2014. 
  8. ^ "Download a Thunderbird that SPEAKS YOUR LANGUAGE". Retrieved March 1, 2015. 
  9. ^ Mozilla Licensing Policies,, retrieved January 5, 2012 
  10. ^ a b "Debian and Mozilla – a study in trademarks".  
  11. ^ "thunderbird breaks half a million downloads in three days". Asa Dotzler's Blog. December 10, 2004. Retrieved February 9, 2013. 
  12. ^ "thunderbird 1.0 reaches 1,000,000 downloads in just 10 days!". Asa Dotzler's Blog. December 18, 2004. Retrieved February 9, 2013. 
  13. ^ a b "Thunderbird: Stability and Community Innovation". Mitchell's Blog. July 6, 2012. Retrieved August 18, 2012. 
  14. ^ a b "Thunderbird/New Release and Governance Model". MozillaWiki. Retrieved February 14, 2015. 
  15. ^ "Thunderbird Reorganizes at 2014 Toronto Summit". The Mozilla Thunderbird Blog. November 25, 2014. Retrieved February 1, 2015. 
  16. ^ "Mozillazine Forums". Retrieved June 18, 2009. 
  17. ^ "Themes :: Add-ons for Thunderbird". 
  18. ^ "MailNews:Supported IMAP extensions". 
  19. ^ "402392 – Support other message storage formats. (prelude to pluggable mail stores)". Retrieved March 1, 2015. 
  20. ^ a b c d e "Limits – Thunderbird". Retrieved 2015-03-08. 
  21. ^ "Thunderbird 3 Planning". August 10, 2009. Retrieved August 19, 2009. 
  22. ^ "793865 – nsIMsgParseMailMsgState.envelopePos must be 64bits to support large mbox folders (eg. 4GB)". 
  23. ^ "Mozilla Thunderbird 24.0 System Requirements". Retrieved November 13, 2013. 
  24. ^ "Mozilla Thunderbird". Retrieved November 13, 2013. 
  25. ^ "mail/thunderbird". FreshPorts. Retrieved August 18, 2012. 
  26. ^ "thunderbird-31.4.0 – Mozilla e-mail, rss and usenet client". OpenBSD ports. Retrieved March 1, 2015. 
  27. ^ "Warpzilla – Mozilla for OS/2". January 8, 2013. Retrieved November 13, 2013. 
  28. ^ "Ports/os2 – MozillaWiki". Retrieved November 13, 2013. 
  29. ^ "Mozilla Thunderbird – Reclaim Your Inbox". Retrieved November 13, 2013. 
  30. ^ Marcel Michelson (December 10, 2009). "French Military Donated Code to Mozilla Thunderbird".  
  31. ^ "QUALCOMM Launches Project in Collaboration with Mozilla Foundation to Develop Open Source Version of Eudora Email Program". October 11, 2006. Retrieved November 13, 2013. 
  32. ^ "Uses Mozilla Firefox trademark without permission – Debian Bug Tracker".  
  33. ^ Claburn, Thomas (July 27, 2007). "Mozilla Gives Thunderbird E-Mail The Boot". Internet section ( 
  34. ^ "Mozilla Launches Internet Mail and Communications Initiative". September 17, 2007. Retrieved June 18, 2009. 
  35. ^ Paul, Ryan (April 5, 2011). "Thunderbird returns to nest as Mozilla Messaging rejoins Mozilla". Ars Technica. Retrieved April 5, 2011. 
  36. ^ Sarah Perez (July 6, 2012). "So, That’s It For Thunderbird". TechCrunch. Retrieved August 18, 2012. 

External links

  • Official website
  • Mozilla Thunderbird project page
  • Rumbling Edge – Tracking developments in Mozilla Thunderbird builds
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