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Please do not edit this page without explicit permission from David Ascher. Your comments are welcome on the Discussion page.

Thunderbird 3 Planning

We're trying to get a better grip on exactly what Thunderbird 3 should look like, so this page reflects some current thinking, but it's still a draft and feedback is encouraged.

Individuals working on the project or interested in the process are encouraged to participate in the newsgroup or find the developers on the #maildev channel on


Goals of the Thunderbird 3 Release

The 3.0 release of Thunderbird has a few high-level goals:

  • To ensure that Thunderbird keeps up with the evolution of the Mozilla platform
  • To increase adoption of Thunderbird
  • To improve usability
  • To facilitate the development, dissemination and use of extensions


Thunderbird 3 is not the last planned release of Thunderbird. As such, many desirable changes will not be included in this release, so that Thunderbird 3 can happen sooner. Planning for Thunderbird 4 will start long before Thunderbird 3 is out the door, along with a longer-term roadmap for Thunderbird evolution.

Platform Update

Because of a combination of:

  • the strategic value in maintaining alignment with the rest of the Mozilla project
  • anticipated performance and feature improvements
  • the continuously improving stability of the trunk, thanks in large part to automated testing policies
  • the relatively conservative roadmap for 1.9.1 discussed in

my (dmose's) belief is that the right choice is to ship Thunderbird 3 on top of Gecko 1.9.1.

Older docs at Architecture Cleanup.

Increased Adoption

I (DavidA) believe that Thunderbird could gain large numbers of users by a combination of improving the out-of-box experience, especially w.r.t. configuration, and by bundling in Lightning.

In no particular order, features to consider include:

  • UI refresh
  • Easier configuration, possibly using one of the ways described in Simple Account Setup or Autoconfiguration
  • Bundled Lightning 1.0, possibly with the GData provider
  • Faster content search
  • Improved address book usability
  • GMail IMAP support
  • Selected additional user experience improvements

Better Extensibility

The extensibility features of the Mozilla platform are one of the strongest assets that Thunderbird has, but there are a few roadblocks towards making extensibility as vital for Thunderbird as it is for Firefox. While this is a long-term goal spanning more than just the client itself, there are some changes which should be done in the Thunderbird 3 timeframe to allow for easier extension writing, publishing, installing and community building.

Architectural Cleanup

Major revisions are always the occasion for refactorings and other architectural cleanups which may have little short-term user-visible impact, but which are needed for maintainability and long-term feature planning. Some of the specific changes being considered:

Finishing Half-Completed Features

There are several features which have partial implementations. These should be reviewed to determine whether the work required to finish them is a good payoff relative to other possible work items. The ones I know of:

Important Bug Fixes

This section should be used to keep track of notable bug fixes which are notable enough that everyone involved in the project should be aware of them. Many other bug fixes will happen as a matter of routine.

Interoperability bugs

  • Support for winmail.dat attachments bug 77811

Delight bugs

Getting Involved

This page should generally not be edited except by the Thunderbird 3 leads (currently DavidA). However, input is welcome, either in the Discussion page, or as additions to the following pages:

Good sources of candidates for the above are: