@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
When SELinux is enabled, this is blocking your connection from the webserver to the Zarafa server.
You may solve this by allowing Apache to make network connections:
or by disabling SELinux altogether:
When you choose to disable SELinux, you will also want to edit /etc/sysconfig/selinux to disable it for reboots too.
Hints en Tips
More information about Selinux can be found here: http://fedora.redhat.com/docs/selinux-faq/