Rainloop is an attractive webmail with a nice clean modern feel to it. After following several different installation procedures, I finally got a working copy.

Assumptions: Apache has already been installed. Sendmail or Postfix is already installed correctly.

Install Rainloop

mkdir /var/www/html/rainloop
cd /var/www/html/rainloop
curl -s http://repository.rainloop.net/installer.php | php
find . -type d -exec chmod 755 {} \;
find . -type f -exec chmod 644 {} \;
chown -R apache:apache .

Create a configuration file for Apache.

vim /etc/httpd/conf.d/20-rainloop.conf

Alias /webmail /var/www/html/rainloop

<Directory /var/www/html/rainloop>
    Options -Indexes
    AllowOverride All
</Directory>

<Directory /var/www/html/rainloop/data>
    Order Deny,Allow
    Deny from All
</Directory>

Restart or Reload Apache

service httpd reload
service httpd restart

Logon to the admin control panel with default credentials.
URL: http://yourdmain.com/webmail/?admin
user: admin
pass: 12345

Among the settings on the add Domains page, use 127.0.0.1 for both with standard ports. Also ensure that there is an [x] for use short login forms and use authentication.