Installing the pre-build packages

deb http://[debian|ubuntu][debian|ubuntu]/ [sid|sarge|sarge_bdb44|etch|breezy|feisty|gutsy] main

to your /etc/apt/sources.list (choose the right value from the square bracket)
so on a Debian Sarge it would look like this:
deb sarge main

and then do
apt-get update
after that exits:
apt-get install citadel-suite

in order to get the packages installed.

Packages available here and their content

At the moment we have i386 and amd64 packages available here.
citadel-serverThe citadel server package. This will become the heart of your system.
citadel-webcitThis will make the webinterface to citadel. You can install that on a different machine. But be sure to check the FAQ!
citadel-mtaThis replaces the system MTA package and provides Sendmail (/usr/sbin/sendmail)
citadel-docInformation about citadel...
citadel-clientThe citadel commandline client. If you like bbs'ish text interfaces, use this.
citadel-webcit-apacheIntegrates webcit with apache and mod_proxy. You would use this if you have several applications and want them be running on the same domain. (NOTE: this is a work in progress and not yet ready for use)
libical0[-dev]The Ical library needed by citadel
libsieve2[-dev]Backport of the Debian libsieve package
libdb4.4[*]Backport of the Berkeley DB 4.4 packages to Sarge

To build from source

add this line to your /etc/apt/sources.list:
deb-src stable source
(add _snapshot if you want to try a development release) then do:
apt-get source libical0
cd libical0-0.26.6
fakeroot dpkg-buildpackage

if it complains about missing build dependencies, install them via apt-get install, and repeat the above step. Then do
cd ..
dpkg -i libical0*.deb
apt-get source citadel-server
cd citadel-<tab>
(to make it expand the version number)
fakeroot dpkg-buildpackage
cd ..
apt-get source webcit
cd webcit-<tab>
fakeroot dpkg-buildpackage

Then install the citadel-* packages you need. You might not want to install the -mta package, if you want to stay with another mail transport agent.