I find it a little bit strange that they didn't realize their solution didn't work before lauching and getting funding. A business idea, or a consumer product

I find it a little bit strange that they didn't realize their solution didn't work before lauching and getting funding. A business idea, or a consumer product can fail or succeed depending on many parameters. But a spam filter is a technical part. There are metrics that can clearly tell you whether it works or not.