Since the migration to Zimbra, using calenders should be much more straightforward than what is described here.
Calendar Option for Linux (&Mac) Users
Since the shutdown of the "Corporate Time" (CTime) calendar tool some years ago, no DESY wide solution for a work calendar for Linux users has come up (although there is talk about a future solution, but it is unclear when this will appear). Mac user can use the DavMail solution described below, too.
The only official calendar is the one from Microsoft Exchange, which you can access from Linux either via the web front-end webmail.desy.de or using the Windows Terminal Server via Outlook. Since both options are not perfect (think of not-working reminder pop-ups), many Linux users use a private calendar, which has the disadvantage of not having the possibility to share events. Further, it is not visible by other group members and the calendar is not being accessible from the outside.
Note: Using a Google calendar for work data is probably critical with respect to legal matters, since the data is stored somewhere in the U.S.
Here, a solution will be described how to set up such a calendar using Lightning in Thunderbird. Further a setup is shown, how to connect the Lightning calendar (or any other calendar tool able to use CalDav) with the official Exchange server.
Setting up Lightning
Lightning is an add-on for the Thunderbird mail client. You can download it via the official file server.
Note: the version offered on the home page does not work with the version 2 of Thunderbird which is pre-installed in Scientific Linux 5 versions at DESY. You can use the links here to download the 0.9 version of Lightning which still works with Thunderbird 2: 32bit machine 64bit machine
For other old Thunderbird versions which are incomplatile with the latest Lightning release:
"Please use the earlier 1.0b7 (Thunderbird 7) or 1.0b5 (Thunderbird 5 and 6) or 1.0b2 (Thunderbird 3.1) or 0.9 (Thunderbird 2.0) release if you still use an earlier version of Thunderbird." quote from the Lightning home page
Search on the pages linked in the above quote for the point "Contributed Builds" to find a link to the 64bit versions (standard download is for 32bit versions).
The add-on is installed in Thunderbird as usual: go to Tools → Add-Ons → Install (at bottom of newly opened window) → choose the downloaded file and install it. The usage of Lightning should be pretty straight forward, some help can be found in the FAQ. Now you can easily create local (=private) calendars on your hard disk.
Tip: If you do not want to switch between the mail and the calendar view in Thunderbird: open one of your mail folders (right click → open) in a new window and choose in this window the calendar view. Older versions of Thunderbird don't remember this layout after a restart, but the ones installed at DESY under SL6 and SL5 (by now) do .
Tip: A file containing the dates of german holidays from 2010-2015 can be found here; this you can import in Lightning via "File" → "Import Calendar".
Connecting to the Exchange server
For the setup that is currently used at DESY (Exchange Server 2003 and Thunderbird 2), there seems to be only one solution to connect the two. This is using DavMail as a local gateway server.
DavMail is a Java program that starts a local server which can read from the Exchange web front-end and offers a CalDav port to Lightning (or any other calendar program that can connect to CalDav). You can download it here (under "Linux (other)", make sure to download the package called "davmail-linux*.tgz" and not the source package!). The installation is described here. You can start the DavMail server by running davmail.sh (for daily use it is probably convenient to create a shortcut on your desktop or add it to the autostart). At the first start a setup menu should appear. How to set it up is described here. Since only the CalDav gateway is interesting in the DESY setup, all others should be un-ticked. For the EAS (Exchange) URL enter https://eas.desy.de/exchange (history: https://owa.desy.de/exchange doesn't work anymore since the introduction of a captcha on the login page; the added /exchange for eas became necessary in March 2014). The settings are shown in the screenshot below (mind that deleting the 90 day limit from the "Calendar Pad Events (Caldav)" increases the network traffic and can slow things down for large calendars):
After a successful start, a symbol should appear in your system tray.
Since the DavMail server is only running locally and per default not open to access from other machines, security impact should be negligible. Of course, you can also setup Lightning and a DavMail instance on your laptop or at home and in this way access the Exchange calendar from "everywhere".
Mac: DavMail runs also on a Mac, so you can use it to connect your calendar to the exchange server there, too.
Settings in Lightning
To connect to your exchange calendar, create a new calendar in Lightning (right click on a free spot in the list of your calendars in the calendar view and choose "New Calendar"). Choose "On the Network" and then "CalDav". Location is of the form:
Replace here "email@example.com" with your official firstname.lastname@example.org email address. Any addition to the URL above like e.g. "/test" would refer to a sub-calendar. On the next tab, you can assign a nickname to this calendar . Login data would be "yourusername" and your normal password.
Now everything should be working. Events entered via Lightning should appear under Outlook and vice versa. For detailed settings (e.g. privacy settings) of your Exchange calendar, you might still have to use the Windows Terminal Server and do them in Outlook, but everyday work with adding/modifying/deleting events works from Lightning.
Tip: If you had an existing local Lightning calendar, you can import it to the Exchange calendar. For this, you first export it (right-click on the calendar in Lightning → "Export Calendar"). Make sure to give the file the ending .ics, else the import dialog won't show it. Then you can import it again by choosing "Import Calendar" in the "File" menu and choose your Exchange calendar to import into (Note: the import may take some minutes, depending on how full your existing calendar was).
Sychronizing your Android Smartphone etc.
To access the calender on an Android smartphone (or pad or...), you don't have to use a CalDav server, but you can directly set up an exchange connection there. For Android, you set the connection details in the included email client and then de-select all the email sychronization. A detailed guide can be found in this Instruction to set up Exchange account on Android. Unfortunately, with the Android build-in apps, this only possible for one account (this means also: only one calendar).
The more or less undocumented address of the DESY exchange server is eas.desy.de.