I found a Java program here Preauth - Zimbra :: Wiki for Zimbra Autologin from Windows.
I got a preauth key from my server.

It might be slightly off topic here, but I don't know how to run a java program from windows.

I pasted the source code in a text file, changed the preauth key and server name, saved it as Main.java. When I do java Main.java on the command line, I get the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: Main/java
Caused by: java.lang.ClassNotFoundException: Main.java
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)

Do I have to put together a .jar file? Can anybody post a solution they have?

Sorry for this beginners question, but I don't do java programming....

- Bernhard