As I have said before, spam is an economic problem. Spam is sent out because it is absurdly fucking cheap and can be profitable for a minimal amount of work on behalf of the spammer. If you want to stop spam, you need to reduce the profit margin for the spammer. There are ways to do this, and google has the access to the proper tools to make that happen. But filtering is not one of those ways. We can play spam filter whack-a-mole until the end of fucking time, or we can look at the problem for what it is and actually try to address it.
Clearly the first option is, sadly, the more popular one by far.