I migrated my mailserver a few hours ago to a complete new system to have a better groupware solution and less noise. But honestly, I am already missing the old patchwork system as its spamfilter was working very very very… efficient. As the new anti spam system didn’t have that much training, the detection rate is simply crap.

Spam is different. Your spam differs from mine. So the filter needs some time to get used to the messages and learn. The result should improve over time quite well.