Maybe it has changed but I have vivid memories of training lots of spam a decade or so ago and still getting half-assed results. Google was the first email provider that really did a good job blocking spam.
There is one setting, underdocumented, which makes a big difference these days. spamc has a default ceiling of 10K, messages larger than which it passes unchecked. Spammers have started routinely including images just over that threshold to defeat default installs. Bump that up a bit, and your accuracy will go way up.
