2003—2010 Originally launched as
Minotaur shortly after
Phoenix (the original name for Mozilla Firefox), the project failed to gain momentum. With the success of Firefox, 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. 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 ten days. 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. Lightning supports the full range of calendar mechanisms and protocols supported by the Mozilla Calendar infrastructure, just as with modern (post-0.2) Sunbird. 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." The project was 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. 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. On September 17, 2007, the Mozilla Foundation announced the funding of a new internet communications initiative with David Ascher of
ActiveState. The purpose of this initiative was "to develop Internet communications software based on the Thunderbird product, code, and brand". 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".
2011—2016 On April 4, 2011, Mozilla Messaging was merged into the
Mozilla Labs group of the Mozilla Foundation. Following in the footsteps of Firefox, Thunderbird switched to a rapid release cycle in 2011. Version 4.0 was skipped so as to re-align Thunderbird with Firefox's version 5.0, both released in June 2011. By the end of the year it had reached version 9.0. On July 6, 2012, a confidential memo from Jb Piacentino, the Thunderbird Managing Director at Mozilla, was leaked and published to
TechCrunch. 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 Executive Chair of Mozilla,
Mitchell Baker, stated Mozilla's decision to make a transition of Thunderbird to a new release and governance model. 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 shifted to Mozilla offering only "Extended Support Releases", which deliver security and maintenance updates, while allowing the community to take over the development of new features. 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 decided that more staff were required working full-time on Thunderbird so that the Thunderbird Team could release a stable and reliable product and make progress on features that had been frequently requested by the community. On December 1, 2015, Mozilla Executive Chair
Mitchell Baker announced in a company-wide memo that Thunderbird development needed to be uncoupled from Firefox. She referred to Thunderbird developers spending large efforts responding to changes to Mozilla technologies, while Firefox was paying a tax to support Thunderbird development. She also said that she does not believe Thunderbird has the potential for "industry-wide impact" that Firefox does. Mozilla remained interested in having a role in Thunderbird, but sought more assistance to help with development. Therefore, at the same time, it was announced that Mozilla Foundation would provide at least a temporary legal and financial home for the Thunderbird project.
2017—present On May 9, 2017, Philipp Kewisch announced that the Mozilla Foundation would continue to serve as the legal and fiscal home for the Thunderbird project, but that Thunderbird would migrate off Mozilla Corporation infrastructure, separating the operational aspects of the project. Mozilla brought Thunderbird back in-house in an announcement on May 9, 2017, and continued to support its development. The Thunderbird development team expanded by adding several new members and overhauled security and the user interface. The interim/beta versions Thunderbird 57 and 58, released in late 2017, began to make changes influenced by
Firefox Quantum, including a new "Photon" user interface. Despite the removal in Firefox Quantum of support for
XUL-based
legacy add-ons in favor of
WebExtensions, the stable/
ESR release of Thunderbird 60 in mid-2018 continued to support them, although most would require updates, and it did not support WebExtensions except for Themes. In 2018, work was underway for planned support in Thunderbird 63 of WebExtensions and to continue to "somewhat" support legacy addons, according to Mozilla. With the release of Thunderbird 68 in August 2019 it now only supports WebExtension addons. Legacy Addons can still be used if a special "legacy mode" is enabled, but even for this, the legacy Addon has to be converted. Alongside the transition,
OpenPGP support was integrated directly into Thunderbird as a standard feature, seeking to supplant the
Enigmail extension. Mainly for licensing reasons, this is no longer based on GnuPG, but on the
RNP library, which has more liberal licensing terms. On January 28, 2020, the Mozilla Foundation announced that the project would henceforth be operating from a new wholly owned subsidiary, MZLA Technologies Corporation, in order to explore offering products and services that were not previously possible and to collect revenue through partnerships and non-charitable donations. As of version 78.7.1, Thunderbird will no longer allow installation of addons that use Legacy WebExtensions. Only MailExtensions are now compatible with Thunderbird. MailExtensions are WebExtensions but with "some added features specific to Thunderbird". Thunderbird 91 features various UI improvements (including a new account setup workflow),
Apple silicon support,
CardDAV address book support, built-in import and export tools for Thunderbird profiles, the
PDF.js PDF viewer, and the ability to encrypt emails to BCC recipients. On June 13, 2022, it was announced that the Mozilla Thunderbird team would take over development of the
Android email client app
K-9 Mail, with plans for it to eventually become a mobile version of Thunderbird with synchronisation support. and in December 2024,
iodéOS, an open source
Android operating system, began including Thunderbird Mobile as the default email client for some 30+ devices.
Releases 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. == Thunderbird Pro ==