Thunderbird got a big boost recently with the news that Ubuntu will be using it as the default mail client in Ubuntu 11.10. If you're getting ready to switch to Thunderbird, or just want to spruce it up a bit, here's a few extensions that will make Thunderbird 5 even more useful.
As desktop mailers go, Thunderbird is usually my favorite mailer. (I tend to switch mailers as much as I hop distros.) There is no such thing as a perfect mailer, but Thunderbird is pretty close. It's even better with a couple of tweaks.
Add Conversations to Thunderbird
One of the things that many users love, love, love about Gmail is the ability to have the conversation view. What's that? If you haven't used Gmail, it groups (or tries to group) conversations in one line in your inbox and folders. For instance, if you're having a long-running discussion on a mailing list with the subject "what should we paint the bikeshed?", Gmail will group all those messages in one line when you view your inbox.
This is one thing that Thunderbird users have wanted for a very long time. To add this, you need to be running a recent version of Thunderbird. (I believe it's 5 or later, but the page is somewhat unclear.)
Conversations have a "first run assistant" that you'll want to pay attention to. Conversations do more than just group subject lines — it does change Thunderbird's behavior in a number of ways that you need to be aware of.
Mandatory changes include turning on global search and indexing, re-indexing messages, and it won't won't expand threads even if they contain unread messages. (Until you expand them manually, of course.)
There are a number of optional changes as well. It won't display attachments inline by default, it searches the sent folders for the unified inbox in Thunderbird, and requires the message pane to be visible.
As you can see from the screenshot, the conversation view emulates Gmail fairly closely. It's not exactly like it, but I do find this view to be much more in keeping with the way I've gotten used to reading mail using Gmail. If you're a fan of the Gmail way of doing things, but don't want to use Gmail exclusively or at all, the Conversations Add-On is pretty useful.
A Little Lightning
You might notice that Thunderbird is missing a few things you find in Evolution, Outlook, or even Google Mail. Namely, Thunderbird doesn't have calendaring or task management.
That can be changed pretty easily, though. The Lightning extension gives calendaring and task management to Thunderbird, and integrates pretty well. You can also use Lightning with other calendaring systems that support iCal or CalDAV.
Using Lightning, you can schedule events, accept invitations, and even turn emails into tasks. I find that particular feature very useful, as it takes the body of an email and creates a task, which means it's easy to clear my inbox without losing my "action items." (And that's as corporate as I care to be today, thanks.)
Want to work with Google Calendar? You might try the GDATA Provider extension. You'll have to do a bit of digging to get your Google Calendar information, but this provider makes it easy to connect Google Calendar to Thunderbird/Lightning.
For the Win: Adblock
Truth be told, I'm not a big fan of Adblock for the browser. While quite a few ads are annoying, sites do need to be able to raise revenue somehow. The same, however, doesn't apply to my inbox.
If you'd like to block ads and filter potential malware in Thunderbird, there's the Adblock Plus Add-On. It's pretty much the same thing that you'd get for Firefox, but it filters out ads and whatnot in mail you receive. (Also useful if you happen to use Thunderbird for reading RSS feeds.)
It's pretty much a "set it and forget it" feature, but you will need to decide which filter to use on first-run. The default is the Fanboy Adblock List. So far, I haven't had any problems with that.
Much Better Bird
As I said, I like Thunderbird out of the box — but I like it much better when blocking ads, conversation view, and the ability to connect to my calendar and create tasks.
I also have to say that I really like Thunderbird 5, and I'm optimistic about the mailer with it getting on the rapid release cycle along with Firefox. I hope that Mozilla is able to get it back on track and get Thunderbird some love, and I really hope the add-on community continues to extend Thunderbird in useful ways!