Though it gets much less attention than its browser sibling, Thunderbird is still plugging away. Since it's on the rapid release cycle, it's also pushing out releases pretty regularly, with fewer new features per release. With Thunderbird 11, it's a very short list of new goodies but a long list of fixes.
Check out the buglist for Thunderbird 11 and it's clear that the Thunderbird team has been busy. But the new features list for 11 consists of a very short list.
With 11, Thunderbird is using a new version of the Gecko layout engine. This should provide better and faster rendering of Web content.
The other big new feature is a change in the way tabs are displayed. In previous releases of Thunderbird, the menu toolbar with buttons for "Get Mail," "Write," and "Address Book" was displayed above the tabs.
This is a modest improvement over the old UI, but I'm still not convinced that Thunderbird has hit on the right design yet. Putting the "Reply," "Forward," and other buttons just above the message display rather than at the top of the Thunderbird UI has never really worked well for me. I wind up customizing the toolbar to add them up top, and removing them from the bottom toolbar.
If you've not been keeping up with Thunderbird, the 10.0 release added the ability to search the Web from the toolbar in Thunderbird and improvements in searching emails. That was out on January 31st of this year.
The Thunderbird 9.0 release, on December 20th added Gecko 9, a feature for sending performance and usability data back to Mozilla, and some minor features related to Personas.
Thunderbird 8.0 was a similarly lackluster release with a handful of shortcuts added, some UI changes, and a switch to Gecko 8.
I'm glad that Mozilla is still working on Thunderbird, but it really doesn't seem to be getting very much love – especially relative to the work that's going on with Firefox.
The change to rapid releases is welcome, but it's been a very long time since Thunderbird really had any substantial improvements.
Thunderbird's IMAP performance, for example, could use a bit of improvement. I find that it's pretty laggy in accessing or working with IMAP folders of any size. I also get, intermittently, errors about accessing my GMail account where Thunderbird reports a wrong password. Unfortunately I can't tell if this is an error with Thunderbird or GMail. As soon as I can reproduce it again, though, I plan to file a bug report.
Sending mail is also a bit sluggish. This may or may not be Thunderbird's fault, but they could background the window when sending so the user isn't staring at a dialog for sending mail for so long.
Overall, the Thunderbird 11 release is OK, but lackluster. I keep hoping that Mozilla will put a little more oomph into Thunderbird development, but as things stand it doesn't look promising.