Zimbra

From Cheatsheet

Zimbra is an AJAX based enterprise MS Exchange server replacement using Postfix, Open LDAP, Apache and other Open Source tools. You have a web interface similar to Outlook Web Access, and also you can POP/IMAP your mail. It has calendaring and other stuff too. You can download the latest version here.

Installation (Debian, others available on download page)

ssh into server
vi /etc/hosts	make sure you have a fqdn (fully qualified domain name), like this, otherwise the install will hang
	127.0.0.1 localhost your.ip.to.thisdomain mail.yourdomain.com mail
get the package	wget http://h.yimg.com/lo/downloads/5.0.9_GA/zcs-5.0.9_GA_2533.DEBIAN4.0.20080815215219.tgz (or whatever's current)
tar xfvz zcs************.tgz
cd zcs<tab>