You should have "All mail" where all mails show, period. I don't mind if you filter some possible spam out to spam folder. That is not the problem. For an example, let's say I receive "Best Buy" emails. I see some in my inbox, then I click on "all mails" to find more. Then that is not everything. When I search "Best buy", suddenly all these Best Buy emails that did not show under any of these, worth of like past year, show up. Why simply Gmail cannot show all emails that comes thru??