There is no 'best' way to spamfilter bad emails. The definition of spam is unknown and being redefined constantly by spamfilters (which is a little different from what recipients think spam is).
The problem is that the process of 'what is spam' is quite complex for humans. For instance: Suppose I gave you permission to send me bulkmail and you only start to use it two years later. Is that spam? For one person it isn't, for the other it is.
I judge a religion as being good or bad based on whether its adherents become better people as a result of practicing it. - Joe Mullally, computer salesman