Lightning makes Thunderbird soar above Outlook for home use, and places it on nearly equal ground in the office. It includes an overhauled interface with easy-to-use buttons for jumping between e-mail and your calendar, LDAP directory support for event invites, and Sun Java Calendar Server support.
Work on the plug-in is now handled by Mozilla as it prepares to integrate its code into Thunderbird for the big Version 3 update coming later this year, but that doesn't mean Lightning isn't ready to be used now. A menu bar for switching between mail and calendar views can live either above or below the folder tree on the left. On the right side of the main pane is a new panel for quickly viewing and managing events and tasks. Events are searchable at the calendar top, and the display of events is highly customizable. Lightning supports multiple calendars, including iCal, and has bidirectional support for Google Calendar with the unfortunately separate Provider for Google Calendar plug-in.
There is also support for Exchange servers, although for enterprise use fans of Thunderbird/Lightning will likely have to talk to the tech support teams to get the servers configured properly. That, of course, is the biggest drawback compared with using Outlook. Old bugs relating to time-zone management and invitation responses have been eliminated, though, making this add-on an absolute requirement for all users, both at home and in the office.