There are not that many good free cross-platform desktop email clients left. If you would have to list them, it is almost certain that you would mention the Thunderbird program, as it fits the bill perfectly.
Mozilla recently decided to move engineering resources away from Thunderbird for use in other projects such as Firefox OS or Mobile. While the announcement has been a sad day for the Thunderbird community, it did not mean the end of development of the program.
The remaining developers and community contributors managed to sneak in a couple of new features in most new releases and made sure at the same time that security and stability fixes were applied as well.
Mozilla announced back in September 2013 that it made the decision to merge the Thunderbird stable channel with the Extended Support Release Channel (ESR). The core reason for the change in release strategy is that Thunderbird stable and ESR releases have been more or less identical ever since Mozilla pulled the development resources from the Thunderbird development team.
A new version naming convention had to be found, and the plan was to merge the channels starting with Thunderbird 24.0. The idea aback then was to increment the digit after the second dot, so that the first version after Thunderbird 24.0 would be 24.0.1.
This naming convention seems to have been changed, as Thunderbird 24.1 has just been released. The next versions of Thunderbird will follow the scheme. ESR users will receive an update from Thunderbird 17.0.10 to 24.2 on December 10 when the next version of Thunderbird will be released.
This means that new Thunderbird versions will only increase the digit after the first dot for the time being. Eventually, Mozilla will move Thunderbird from version 24.x to version 31.x to sync the version of the browser again with the Firefox release schedule.
Thunderbird 24.1 features three core issues that have been fixed:
- Fixed a issue when signatures where difficult to read because they were shown in lighter gray.
- Fixed an issue with Auto CC where it may not have worked if the CC and the sending address were identical.
- Fixed several security issues in Thunderbird.
As far as security fixes are concerned, the new version of Thunderbird fixes five critical, 2 high and 2 moderate security vulnerabilities.