All anti-spam systems have non-zero false positive rate. It is hard to fix all FP in advance, but relatively easy to do this on case-by-case basis. When an FP a

All anti-spam systems have non-zero false positive rate. It is hard to fix all FP in advance, but relatively easy to do this on case-by-case basis. When an FP affects some large sender it gets fixed. When it affects small senders - it is ignored because Big Corps don't care about small fish. They would be happy if all small mail servers will disappear and the market will be controlled by a few big companies.