There are now more and more viable corporate messaging and collaboration systems about, and exchange andmins looking to "escape" have many more options than a few years ago. There are a lot out there, but I have narrowed it down a bit by specifying some requirements. A lot of small businesses need a simple way to administer emails, this in itself is good enough for a lot, add shared calendars and contacts and we have a winner. Make it web based and its even better. Being web based means that the client runs on any OS, and now that you have an "any-OS" client the move to another OS is a lot easier: no user retraining, need for any installation, etc.
Zimbra
This is the open source edition, there are "plus" versions which this can be upgraded to, but this gives us a really decent system for free. Check out the standard and professional versions too though: they make life a lot easier with some nifty extras like online backups and outlook integration to name a few, at pretty reasonable prices . It has a very good looking AJAX web gui, so no extra clients are needed either. The installation is on Ubuntu Dapper, best for server type installs because of the nifty support term (it will get security updates till 2011).
Install Ubuntu 606 LTS (server)
A simple install, just boot the server CD, choose "Install to the hard disk" and let it run. To prepare for the zimbra install, we also need to install a couple of packages:
sudo apt-get install libidn11 curl fetchmail libgmp3c2 libpcre3 libxml2 perl libexpat1
Install Zimbra
Get the open source edition from http://www.zimbra.com/community/downloads.html- there is now a "formal" ubuntu version for the communtity and network editions. Untar, and run the installer as root.
wget http://your-mirror/file.tgz untar zcs-4.0.3_GA_407.UBUNTU6.tgz cd zcs sudo ./install.sh
This will kick off the installer, its a pretty straight forward install, just follow the prompts. You will need to set an admin password at the end of the install, select option 6, then 4 and choose a password (may be different on your install). Take some time to read over the options, there are a couple there that are very useful, like https mode etc. Once its all done, it will suggest you press "a" to apply settings. Once all this is done, it will start the services and you are ready to roll.
Gotchas
DNS: Be careful to make sure you have your DNS set up correctly. Your hostname will need to resolve to localhost (check your /etc/hosts to make sure you have a 127.0.1.1 line with your fully qualified dns name. The mail hostname can be anything, make sure its correct during install. If your internal DNS servers give a different MX record for your domain, it will moan, also, it may get the external ip of your router when it looks for MX records for the domain you are using.
Configuring: Be careful with configuring the component services like postfix as you normally would (postconf etc), as there may be zimbra-specific tools to do this with. Check the online docs for pretty decent instructions.
Configure Zimbra
Open the admin console on https://yourzimbrahost:7071 - add some users and modify the settings to taste. Users can use the very slick web interface at http://yourhost (or https if you configured it like that) or any imap or pop client. Thunderbird can view the calendars with the lightning extension (although the web interface is much prettier!), so you can have a completely open set of apps from the server down to the client.
Opinions
PLUS: The web gui is very slick, and this will definately be a good selling point to manager types where shiny==quality, you will probably get the same with users who may be used to their old client but like new toys. The OSS version is completely free and pretty functional, within 15 minutes you can have a fully running, good looking web based mail and collaboration server for just the cost of your time. Standard components like postfix, mysql, tomcat etc, no re-invented wheels to learn! Good, extensible anti-spam and anti-virus with amavisd-new.
MINUS: Backups seem to be left behind a bit in the OSS edition, so either upgrade to network edition, or swat up about the various backup options available.
The sexy AJAX web interface for Zimbra
