Free software tools for ensuring email security and managing spam are good and self-managing, but they can be difficult to set up. This was proven by a recent prod to investigate options.
Edited, September 2016 - I have reluctantly reverted to other anti-spam systems. Debian have stopped providing dspam, although there is a more recent version than the last packaged version. Worse, the version that is packaged for the Raspberry Pi, which has most to gain from dspam, does not work. This is a great pity, as dspam, for the 15 months I have used it, is accurate (96.20%), lightning fast, and uses very few resources.