Zimbra Server is an email and collaboration server for Linux or Mac OS X. It can run email, group calendaring, address book/contacts software, and instant messaging, as well as deal with file and web document management. 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 installed.
In the end I had to edit util/utilfunc.sh to replace libgmp3 with libgmp3c2. Different package names should be recognized according to your platform for the supported platforms. Before the package installation stage, I was also asked to edit /etc/hosts. The line need contain only localhost, not any hostname.
Having sorted the package name problem out, the lack of Debian 5.0 support causes another installation abort a few stages down the line. To get past this, edit util/modules/packages.sh to include this line:
just above the line where it checks what $PACKAGE is. You'll then need to run ./install.sh --platform-override (and hit 'Y' when you get to the 'install anyway?' question). You also have to downgrade a set of Perl packages to Etch (see this helpful blog post – you'll need to download the old versions manually and install them with dpkg -i.
Obviously, these issues are the price one pays for trying to install on an unsupported system. However, Debian lenny has been out for a while now (and has been available as testing for much longer!), and I'm not terribly impressed by a piece of software that requires an older version of a very common distro.
Once I got past these problems, the install itself was pretty straightforward. Most things are managed for you, and the questions asked are handled clearly. It claims to need 5GB of space, but I was able to install it without any issues onto a filesystem with rather less spare than that (3.6GB) using the -x option. Obviously, if you're running it seriously, the data is likely to start eating up space.
When doing the final setup (as per the quick start guide on the web site), it complains if you're using Iceweasel (apparently it's not recognized as being Firefox-equivalent), but it doesn't actually stop you from logging in, and setting up a new account is easy. Note that you'll also need to set the password separately before the user logs in.
The admin console is quite slow, although this would doubtless be less of a problem on a newer machine than mine. It's Java-based, so performance will depend on how well the virtual machine is tuned for your particular setup.
Having set up the basics, I downloaded Zimbra Desktop to try the end-user experience. It appeared a bit ugly while doing the initial setup, but once the desktop itself was running it was fine, and setup (both initially and thereafter) was straightforward. The default settings for mail and others seem sensible (mail is text-only by default!), but the tab order wasn't set on at least some panes, which is irritating. Bizarrely, there seems to be no way to start the client up over a remote X connection – it runs as a background service and is accessed via the menu bar at the bottom of the screen, which you don't get when running X over ssh. (Or at least, I couldn't find any other way of getting at it.)
Being only one person, I was limited in how much I could experiment with the group calendaring and other similar things. However, Zimbra Desktop has iCal feed integration, and it seems to be possible to sync between Google Calendar and Zimbra and to import Google Calendar feeds so you can see them within Zimbra. There are plenty of options for sharing documents, calendars, and so on: It's structured very much like standard connectivity software. I liked the "Tasks" list option — handy to have your to-do list interoperable with your mail, calendar, and shared documents!
Zimbra Server looks has much promise. In particular, if you're looking for a desktop-based calendaring/sharing solution that operates in the same sort of way as Outlook, then it's worth investigating. However, I think it's a real shame it doesn't support server installation on Debian stable – hopefully this will be updated soon.
Note: This was written prior to the release of Zimbra 6.0. There are several end-user improvements in the new version, including a read receipt option and some calendar usability improvements. There's also more integration for zimlets — like the Zimbra Social zimlet that hooks into various social apps such as Twitter. So now it's even more worth checking out!
It may sound odd offering more Zimbra installation advice since there is a lot on the subject in other blogs, our documents, wiki and Forums. In fact, some quick research surfaced over 1.4 million hits for Zimbra server install on the web and 36,000 on the Zimbra site alone.
But we are also fortunate to have more new Zimbra users than ever, and after helping some trial customers recently, it was a good reminder a few simple tips can help cut through some noise and avoid time-consuming snags once you start the install process. So without further ado here are the top 6 common pre-requisites to consider when preparing for your Zimbra installation:
1. Firewall
Servers have firewalls configured once the operating systems are installed for security purposes. Our recommendation is to temporarily disable the firewall on the system during a single and multi-server Zimbra installation. An alternative would be to refer to our installation guide to get a list of ports (see Table 1) used by the application and make sure the ports are open prior to installation.
2. DNS setup
All Zimbra configurations store hostnames. We do not have save any IP address information in our configuration. The advantage is this allows an administrator to change IP address (more likely) on the Zimbra system without having to perform any application changes.
This scenario means that all the hostnames to be used in a Zimbra installation have to be defined in DNS. Both A and Mx records for the hostnames and email domains need to be defined and verified prior to beginning your installation.
One other thing to consider is split DNS configuration if you are dealing with servers separated by a firewall.
3. Use of Fully Qualified Hostnames (FQDN)
It is crucial to use a Fully Qualified hostname during the Zimbra configuration. For example, you should enter server1.domain.com instead of server1. This avoids incorrect DNS address lookups and ensures that the client would be connecting to the right application.
4. Port Conflicts
Standard server configuration comes with support for numerous services like POP, IMAP and HTTP (see Table 1). These services are also installed with the Zimbra Network Edition. Therefore, you want to make sure you disable all these services prior to installation. The Zimbra installation scripts will check for any of these port conflicts and notify you to turn these services off before continuing.
5. Libraries and additional packages
Zimbra’s rich feature sets are dependent on additional packages being installed on the system. These packages vary between Linux and Mac Operating system. The Zimbra installation script does perform checks to verify all the dependencies have been met, but going through the System Requirements documentation (available on the Zimbra website) before will save you some time.
(Based on ‘Mailbox Usage of 200 MB’ and 500 users)
+ User Data: 500 users with 200 MB = 100 GB user data
+ MySQL data: 5% of 100 GB (User Data): 5 GB
+ Zimbra binaries: 10 GB
+ Zimbra logs: 20 GB
+ Zimbra indexes: 25% of 100GB (User Data) = 25 GB

SUBTOTAL: 100 + 5 + 10 + 20 + 25 = 160 GB
Backups: 160 % of Subtotal: 160 * 160% = 256 GB for backups
TOTAL: 160 + 256 = 416 GB
6. Sizing
Storage sizing is important for an excellent performing Zimbra application (see example). If you are doing a Network Edition trial you should contact the Zimbra technical team for sizing information for storage including number of disks, which Raid level to use, and the size of the drives to use. Configuration of the Zimbra store volume is important in satisfying the application IO requirements.
Remember, it’s also a good idea to review the Zimbra Quick Installation Guide where you can find this information and many more good tips. 
3How to install Zimbra Server 6 (Release) on Ubuntu Server 9.04 (Jaunty) !