One needs to check the anti-spam facility at your ISP from time to time. Very occasionally I have discovered important emails in the ISP trap which, by any measure of human reason should have been passed on without so much as a blip. A couple of times this has been quite serious and important information has been delayed. (My ISP consistently has one of the highest customer satisfaction ratings in the country).
I have also used Mailwasher almost from the time it was first released. I consider it to be an essential part of my internet software - even though it may be a last resort from a technical aspect.