So, what have we learned throughout this series? For one thing: Lose No Mail. This is the primary function of the E-mail administrator, but it's the easiest one to forget as you get mired further and further in the fight against both spam and viruses. On top of this, you're expected by all those other picky administrators to keep your network from spewing spam out by locking down relaying and other spammer favorites, and now you're even expected to set up your servers so that they stop spam and viruses from ever reaching reaching your users' desktops!
Hopefully, after you stopped hyperventilating, you managed to reach the point where we discussed the many tools available for both Windows and Unix administrators. There's a heavily active anti-spam movement out there, so you'll find that once you start digging, there's plenty of help on the tools we discussed, not to mention a whole lot of tools that we didn't have a chance to talk about (and that we may not even have heard of, since there's only so much time in a day).
Just be sure that you combine whatever new solution you choose with a bit of user education. Whether you're adding quarantine management to the mix or not, there will still be some kind of quarantine involved where the suspected spam is trapped. Users need to know that this place exists, and how to either look in it for mis-diagnosed E-mail, or how to ask someone else to if they suspect that some important E-mail was lost.
Get your users to buy into the process, and watch everyone's productivity soar while their frustration melts away. Though, there won't be so much entertainment anymore from reading the more ridiculous spammer come-ons as they arrive in your inbox.