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.
The 11 is for people with the pride of a 10 and the pocketbook of an 8. -- R.B. Greenberg [referring to PDPs?]