The spam problem has never been solved, no matter how good spam filters may have become in the recent years. It's still an arms race, with a front that is moving one way or another every few months. Even today, a spam filter is a piece of software that you trust to throw away e-mails without letting you read them, based on its own decision that you don't want to read them.

It seems insane to me that people would willingly let a program decide to throw away inbound mail based on unspecified rules. And I nearly start frothing at the mouth when someone suggests that, since their software decided to throw away my e-mail, it is somehow my responsibility to fix that. It isn't.

If there were thousands of different anti-spam solutions, and one of them behaved badly, then senders wouldn't care, and users would vote with their feet (or wallet, or app store) until the behaviour was fixed. But since Google has a near-monopoly on e-mail, it's now up to the senders to do the work and jump through the badly-documented ever-changing hoops.