"There's a (free) Zimbra desktop client available, and the
server can also sync with Outlook and Thunderbird. A free and open
source version of the server software is available that doesn't
include support or software subscription. The alternative is to pay
the company for a couple of extra features and support (see the
comparison table for more information about the different
versions). The FOSS version of the sourcecode is under the Yahoo
Public License, and the binaries are under the Zimbra Public
End-User License Agreement.
"Note that you must turn off all currently running LDAP, web
server, mail server and other software when you install Zimbra. It
makes various system changes that may break other apps. So really
you want a dedicated server for it (which may or may not be a
nuisance depending on your setup).
"As always, the first hurdle to clear is installation. I tried
the Debian 4.0 binary: Unfortunately, there's no version for the
current Debian stable release. As this isn't a proper Debian
package, it can't install requirements, only tell you about them,
so you may need to install a couple of packages via apt-get.
However, the lack of correct platform information means the package
names aren't necessarily correct. The install requests libgmp3,
whereas what is required is libgmp3c2, which was already