I think gmail spam filters were OK at the beginning, because spam was so blatant at the time. Nowadays we have both more use of commercial services in valid ema

I think gmail spam filters were OK at the beginning, because spam was so blatant at the time. Nowadays we have both more use of commercial services in valid email, and spam became more sophisticated. As a result, whatever they used to do is just not enough to flag email with high certainty.