You'll need to set up a network calendar, e.g. a Google Calendar, in Lightning on each computer.

Aha. What's a network calendar?

Are they safe? I have to use classified information on appointments.

I have to use classified information on appointments.

I suppose then a Google Calendar isn't the way to go for you. Talk to your IT folks.

OK. Thanks for Your time!

Caldav is the protocol used for network calendars. So you will be looking for a caldav server that meets your security needs. As you have already been told, Google offer a free caldav service, Yahoo and GMX do as well.

However is your information is truly classified than you will be needing a caldav server within your organizational control. This open source project offers introductory information in a simple manner http://calendarserver.org/

Wikipedia offer a fairly good list of server software to provide the server side implementation, along with many clients (Thunderbird/Lightning among them). But like anything you will probably need to involve the network admin folk to determine what can and can not be done in your organization.

This works for Thunderbird/Lightning calendar files (.ics files). It should work on any computer that can run Thunderbird with the Lightning calendar and Dropbox. I have Dropbox installed on my Mac and on a Windows 7 netbook. I put my own calendar file and the USA Holidays file in my Dropbox folder. Any changes I make using either computer automatically updates the file for both computers. It works like a charm. You need to find the calendar files you want to sync and move them to your Dropbox folder. On all the computers you want to sync use the Open Calendar File menu item in Thunderbird and open the file from your Dropbox folder, then delete the original calendar file. You don’t have to deal with figuring out how to use a WebDAV or CalDAV setup and it may be more secure. The tricky part is finding where the calendar files are stored on your computer. I made the switch a long time ago so I don’t remember exactly how I did it so I am including some info I found online on how to do it on both Mac and PC computers. I’m not sure how accurate the info is and you may need to search for instructions for your particular computer and OS. In any case it is really worth the effort. Good Luck! ————— Find Your Mozilla Thunderbird Profile Directory To locate and open the folder where Mozilla Thunderbird keeps your profile including settings and messages: On Windows: 1 Select Run... from the Start menu. 2 Type "%appdata%" (without the quotes). 3 Hit Return. 4 Open the Thunderbird folder. 5 Go to the Profiles folder. 6 Now open the folder of your Mozilla Thunderbird profile (probably "********.default" where the '*'s stand for random characters) and the folder beneath it. On Mac OS X: 1 Open Finder. 2 Press Command-Shift-G. 3 Type "~/Library/Thunderbird/Profiles/". 4 As an alternative: 1 Open your home folder. 2 Go to the Library folder, 3 Open the Thunderbird folder. 4 Now go to the Profiles folder.

CloudyTom said You sure did make your change long ago. Lightning does not use local ICS files anymore.

Well Matt, thanks for your reply. I'm sorry I took up so much space here with old info. But, my solution is still working fine and I just updated to the current versions of Thunderbird and Lightning. Now I'm really confused. Are you saying a new installation of Firefox and Lightning would not install any .ics files? It seems .ics files are still supported though. What file type is being used now? Wouldn't copying those files to Dropbox per my solution work or is CalDAV the only way to go now? I hope this is still pertinent to this thread since it is still dealing with syncing calendars. I stumbled on this question while looking to sync Lighting info with my new Android tablet, but that's another story.

To cut a long story short. Lighting uses SQLite databases internally to Thunderbird.

ICS files can be imported and exported, but write access it problematical

Using dav is simple (as long as you have the endpoint URL.) Reliable and works with mobile phones and tablets as well the lighting.

Your comments about it's security are I think overkill. Communications with a dav source are encrypted and in the case of Google use oAuth2.0 which is about as secure as web traffic can get. Your dropbox traffic will only be secured by SSL.

But I digress. Yes, caldav is the way to go, and it will fix your problem of synchronizing your tablet as well. The only caveat is apple icloud hides the caldav endpoint and you will need to do some digging in the apple support forums for instructions on how to find it in ~\library