Thunderbird Indicator is an add-on for Mozilla Thunderbird which notifies you of new mail messages via Ubuntu's standard notification system and the Messaging menu. Once a new mail is received, the Messaging menu's icon turns green and a notification pops up. The Indicator Applet also provides quick access to your contacts and allows you to compose a new message.
A while ago we were telling you about a PPA that provides a package called "xul-ext-indicator" that integrates Thunderbird in the Ubuntu Messaging Menu. This is actually a Thunderbird extension packaged in a .deb so you can easily get updates.
Until now, "xul-ext-indicator" (Thunderbird Indicator extension) displayed a notification (using the Messaging Menu and NotifyOSD) for emails that arrived in your inbox so if you used filters for your emails, the extension failed to work. But a recent update fixes this so Thunderbird Indicator can now display notifications for emails received in any folder. If you want the old behavior (to only display notifications for emails arriving in your inbox), there is an option in the Thunderbird Indicator preferences:
To install Thunderbird Indicator in Ubuntu (the "fixed" version is only available for Ubuntu 11.04 for now), use the following commands:
sudo add-apt-repository ppa:ruben-verweij/thunderbird-indicator
sudo apt-get update
sudo apt-get install xul-ext-indicator libnotify-bin
The latest version is only avilable for Ubuntu 11.04. In Ubuntu 10.10, you can try to install the 11.04 package or download this .deb I've created for Ubuntu 10.10 last week (this is the one I'm using - ignore the version number, it's actually 1.4).
Thanks to Radu for the screenshot!