Yesterday I used CPAN to install a more recent version of SpamAssassin. I was using a 2.x version which was extremely outdated, so I removed that one first, manually. After installing using ppm (Perl Package Manager) on Esme her Microsoft Windows XP system I tested the new version with my Castle Amber mail account, which gets quite a lot of unwanted bulk email (spam).
I programmed quite some time ago a small Perl program that downloads one by one email messages using the POP protocol version 3 (Post Office Protocol, see RFC 1725) and uses SpamAssassin to classify the email into either ham or spam. Oddly enough, after the update the classification was working badly. After some checking, it turned out that the CPAN installation didn't install the rules and configuration files (at least on the Windows XP system) so only my user rules were being used. Maybe I did something wrong when removing the old version of SpamAssassin.
So I downloaded the gzipped tar version of SpamAssasin with the same version number (3.0.1) from http://archive.apache.org/dist/spamassassin/. I used nmake to make and install this version over the already installed version, and that did the trick. And a new test made clear that not only it worked, but also that the 3.0.1 version worked much better compared to the 2.x version I used. Also, I am afraid that my SpamAssassin cookbook must be quite outdated by now.