People look in their spam folder. Are you sure? I'd be willing to bet that the majority of users either don't know the spam folder exists or trust it to be a o

People look in their spam folder. Are you sure? I'd be willing to bet that the majority of users either don't know the spam folder exists or trust it to be a one-way black hole dustbin they never feel compelled to dig around in. False positives are more likely to be discovered when reported by the sender directly to the recipient via other means than email. Even then, I'd be surprised if half of them followed up by trying to locate the message in the spam folder. Frequency of checking seems like an unreliable metric when most users live in the INBOX, especially when Google virtually organizes the messages into "conversations" for them.