> Is it strictly-true that anti-spam algorithms must be hidden to be effective? No. But that "no" is missing some qualifiers. It's not strictly true since you

> Is it strictly-true that anti-spam algorithms must be hidden to be effective? No. But that "no" is missing some qualifiers. It's not strictly true since you can implement some out-in-open options such as paying money, requiring a phone number, validating your physical identity, delays of use on new account creation, etc, that will make the barrier of entry for spamming much higher. There will still be spam, but it'll become more manageable to manually monitor and take action against. The downsides I feel are obvious based on the service we are talking about. But I would say it is strictly true that you cannot have a free, anonymous, low barrier to entry service without hiding your anti-spam algorithms. There is fundamentally no difference in such an environment to differentiate a bot from a human besides the message content and patterns in who they message. If bots know what content they can't send or what patterns in messaging to avoid, they can still spam.