The latest version of the free software has the two Gmail features I like most: The ability to add multiple descriptive tags to messages and to "star" the important ones. Thunderbird 2 is an improvement over its predecessor.
But Thunderbird is no Gmail.
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Although I had long found Web mail clunky and less versatile than software residing on the computer desktop, all that changed over the past few years as Google Inc. (GOOG) revolutionized Web-based e-mail with its Gmail service.
Rivals soon followed to make their Web interfaces on par with desktop programs.
I've come to rely on Web mail the more I move about, as desktop-based programs generally do not have good mechanisms for synching messages between computers.
In a nod to Gmail's popularity, Thunderbird 2 offers an easy way to bring Gmail messages into the software.
But you previously needed to look up and fill in various port and server settings; Thunderbird fills all that out for you when you select "Gmail" as your account type.
Thunderbird also sports "tags," akin to Gmail's "labels," as a more convenient way to organize messages.
E-mail programs have traditionally relied on folders, and I've had to pick one or make copies of my messages to place in multiple folders.
With Gmail, I can add as many labels as I want — for example, organizing messages based on both whom I'm talking with and what I'm talking about.
Gmail also lets me add stars to messages, handy for keeping track of things to do.
Thunderbird 2 doesn't ditch folders completely, as Gmail did, but it does let you append one or more "tags" to messages.
The new Thunderbird also lets you "star" key messages — more easily accessible and visible than the "flags" from previous versions.
Unfortunately, Thunderbird can't grab the labels and stars you had painstakingly entered into Gmail. You'd have to start from scratch and re-enter the data.
The Thunderbird tags are also more difficult to use.
Whereas Gmail adds all your labels in alphabetical order next to each message's subject line, Thunderbird tags appear in the order they were entered, and by default you see them only by clicking on a message first.
To see them with the list of senders and subject lines, you'd have to click on a small box someone had to point out to me.
I also overlooked the mechanism for sorting messages by tag, the way Gmail lets you grab all such messages by clicking on a label's name. Enabling it required customizing the toolbar and dragging over a box marked "view." Go figure.
Because most people don't mess with default settings, these features ought to be enabled from the start for tags to be truly useful.
I like that Thunderbird lets you add a tag simply by entering a corresponding numeral, but you only get nine slots and can't choose which gets one.
Unlike Gmail, you can color code tags, so that "important" messages automatically appear in red; however, only one color gets assigned when multiple tags are used, and you don't get to choose.
Thunderbird 2, which comes from the same open-source community that makes the Firefox Web browser, offers a number of improvements over its predecessor.
As you can with Web pages in a browser, you can use the "back" and "forward" buttons to return to messages you've read earlier, even if they are in different folders or from different e-mail accounts. Gmail doesn't offer this.
The new version of Thunderbird also promises a better anti-phishing tool and displays more detailed alert windows when new messages arrive.
I can also save frequently performed searches and filter folders so that I only see my favorites, most recently used or those with unread messages.
These features are good, but not flawless: Folders don't automatically update the way I'm used to with newer Web-based interfaces (I'm told some of that is by design based on user feedback).
Where Thunderbird and other e-mail programs shine is in the ability to sort messages by subject and sender, not only by date as with Gmail.
The feature is not new, and it's one I've missed since fleeing for Gmail (Yahoo, Microsoft's Hotmail and Time Warner Inc.'s (TWX) AOL do give you more sort options on the Web).
Thunderbird also gives you continual access to your old messages, even when your e-mail service or Internet connection is down, something that has been happening a lot lately with both Gmail and my Time Warner Cable connection at home.
I'm also heartened by some of the things the Thunderbird team has planned.
Developers want to better synch messages and tags with Web mail services, if they can get the necessary technical hooks from those services.
The team is also exploring easier access to tagged messages through temporary folders.
If your current message is tagged "to do" and "work," two folders with "to do" and "work" messages would automatically appear.
Move to a message tagged only "to do" and the "work" folder would instantly vanish.
That would be an improvement over Gmail's long list of labels.
But until then, I'll upgrade to Thunderbird 2 and continue to download my messages as a backup only.
For my primary e-mailing, I'll stick with Gmail.