Yes, today's tip is about Yet Another Messaging Server. This time Citadel. And why not? The free/open source software world is full of messaging servers, and many of them are also free of cost. Both the free and commercial FOSS messaging suites are more stable, easier to manage, and sometimes capable of handling bigger loads than the Big Gorilla of groupware, Microsoft's Exchange server.
Some old-timers may recognize the Citadel name from the olden BBS days. Yes, it's that same Citadel, only all grown up and with loads of new stuff. It still includes the BBS software, and the Uncensored!BBS is still running.
Citadel is also Groupware's Best-Kept Secret. It's a genuine turnkey messaging suite install it and start using it. No muss, no fuss; just a nice integrated package all ready to go to work.
The fast, easy way to get up and running quickly is to use the Easy Install utility. This pulls in all dependencies and does the builds for you. It's also your updater when new Citadel versions are released. You don't get any customizability with Easy Install, so tweaks must be built manually from sources.
Citadel comes with all the goodies expected in groupware: IMAP, POP3, SMTP, group calendars, contact lists, to-dos, shared folders, and an instant messaging client. It supports all the usual stand-alone mail and groupware clients, like KMail, Evolution, and good old Outlook. Even better is WebCit, its Web client interface. If you standardize on Firefox, you'll have a single cross-platform client to support and no client configuration drama.
Citadel is amazingly scalable, both sideways and upward. It will handle as big a load as the hardware supports. When the hardware starts to complain you can set up a second Citadel server to share the load. For all the power and features, Citadel is a tiny little thing, weighing in well under 5 megabytes with all bells and whistles. Get all the goodies at Citadel.org.