If you have a client app that you think is reliably filtering spam, then to be blunt: you aren't receiving any spam, at least to first approximation. My stack of stuff on my three decade old personal account has a 95%+ hit rate (something I might naively be tempted to label as "reliably filtering spam"), and I see see more spam than signal in the inbox.

GMail, on the other hand, is damn close to 100%. And it does it through excruciating application of heuristics like "don't trust agents that don't set SHOULD headers".