Download and install packages listed on the sidebar:

ECM2 is in beta status. It is stable enough to run in a production environment, but because it still requires some functions to be added and changed it will be kept as beta for a while.
There is a discussion board about the installation.

Prerequisites:

PHP - Apple installed php version 4.4.1 or higher. If you've installed php5 based on php5 installation or downloaded an alternative package such as from entropy.ch to '/usr/local/php5' directory, you have to install Pear DB.
curl -O http://download.pear.php.net/package/DB-1.7.13.tgz
gnutar -xvzf DB-1.7.13.tgz
cp DB-1.7.13/DB.php /usr/lib/php
mkdir /usr/lib/php/DB
cp DB-1.7.13/DB/* /usr/lib/php/DB
MySql - Enable Mysql on your 10.4+ OS X Server according to Apple's instructions. Or if you install it for the first time on OS X 10.4+ Client follow these instructions. In both instances, the location of mysql socket file must be at '/var/mysql/mysql.sock'. No "symlink" from /tmp directory is acceptable.

After downloading the packages, you will have to follow all steps of the installation procedure in order to make this mail-system functional.

All versions of ECM previous to ECM2 are now considered obsolete and everyone is strongly recommended to switch to ECM2 with a brand new installation.

1. Installing SpamAssassin

It is necessary to have Xcode installed. A free ADC Online membership provides access to the latest Xcode. If this is a new Tiger installation, you'll have to initialize perl and install a few modules before you can install SpamAssassin (Login as "root"):
sudo cpan

install Bundle::CPAN 
install HTML::Parser 
install Net::DNS
quit
Install DBI_1.48 and DBD_Mysql-3.0002 packages before you continue installing SpamAssassin via terminal.
sudo cpan
install Mail::SpamAssassin
quit

2. ECM2Admin

ecm2Admin should be in your home (root) directory unpacked:

Set up MySql database via terminal:
mysql -u root -p
mysql> CREATE database ecm2_db; 
mysql> use ecm2_db;
mysql> \. /private/var/root/ecm2Admin/ecm2_db.sql
mysql> quit
After you finished with mysql installation, move the "ecm2Admin" folder to wherever you serve files via apache.

3. Configuration files

EXIM: Open exim "configure" file and edit the top part of "Main configuration Setting":
open -e /usr/local/exim/configure
Fill in username and password, server ip number and your primary hostname:
SERVER_IP = 0.0.0.0
primary_hostname = example.com
hide mysql_servers =
localhost::(/var/mysql/mysql.sock)/ecm2_db/username/password
COURIER (Authlib): Open courier "authmysqlrc" file to edit the following lines near the top:
open -e /usr/local/courier-authlib/etc/authlib/authmysqlrc
MYSQL_USERNAME username
MYSQL_PASSWORD password
SPAMASSASSIN: Open SA's "local.cf" file and edit with appropriate values:
open -e /private/etc/mail/spamassassin/local.c
MYSQL_USERNAME
MYSQL_PASSWORD
ECM2ADMIN: Open "config.inc.phpf" file and enter database username/password:
open -e /Library/WebServer/ecm2Admin/config/config.inc.php
MYSQL_USERNAME
MYSQL_PASSWORD

REBOOT

After you finished with the installation you can log in via web browser at http://yourdomain.com/ecm2Admin.
Inital username/password will be username: siteadmin and password: change in order to gain access as an administrator to set up admins and domains.

When ECM2 is installed and correctly functioning, it sends a new email to the postmaster and/or users upon creation of their accounts. The initial email can be customized within the config file (config.inc.php) for ecm2Admin.