That is not a requirement specific to Google. Most inbound SMTP services require this, even most open-source implementations. This requirement is not invented b

That is not a requirement specific to Google. Most inbound SMTP services require this, even most open-source implementations. This requirement is not invented by Google, but caused by spammers using botnets. Also, not being able to set a reverse DNS for a domestic IP is not Google's fault, it is your ISP not allowing you to 'own' an IP, and not allowing you to set a reverse DNS for the IP they lease to you. This is why ISP offer business packages. These will allow you to own the IP (block), and set reverse-DNS for it.