Since there are no packages available for Debian based distributions, here's a short guide how to easily install CommuniGate Pro 6.0 on Ubuntu LTS 12.04.

First of all, we need alien to convert the .rpm based installer to a dpkg compatible format:

aptitude install alien

Now download and convert the CGP installer:

cd /tmp/  
alien CGatePro-Linux.x86_64.rpm  
dpkg -i cgatepro-linux_6.0-10_amd64.deb

Backup existing mail binaries, so you can restore them in case you uninstall CommuniGate:

mv /usr/bin/mail /usr/bin/mail.ori  
mv /usr/sbin/sendmail /usr/bin/sendmail.ori  
ln -s /opt/CommuniGate/sendmail /usr/sbin/sendmail  
ln -s /opt/CommuniGate/mail /usr/bin/mail

To fix the provided start/stop service on Ubuntu, we need to customize it a little:

sed -i '2,11d' /opt/CommuniGate/Startup # only extract LSB header
sed -i 's/\#\!\/bin\/sh/\#\!\/bin\/bash/g' /opt/CommuniGate/Startup # use /bin/bash instead of /bin/sh Shell  
sed -i 's/\ 3\ 4\ 5$/\ 2\ 3\ 4\ 5/g' /opt/CommuniGate/Startup # fix start runlevel
sed -i 's/\ 0\ 1\ 2\ 6$/\ 0\ 1\ 6/g' /opt/CommuniGate/Startup # fix stop runlevel

Last but not least, we can move the start/stop script, change it's permissions and make it start automatically on boot:

mv /opt/CommuniGate/Startup /etc/init.d/CommuniGate   
chmod +x /etc/init.d/CommuniGate  
update-rc.d CommuniGate defaults