That’s not how email works. Your email provider maintains servers to send and receive messages on your behalf, and your email client checks in with your provider for messages. iMessage not like email.
On iMessage, all messages are stored on Apple’s servers (at least in-transit), even those that would be destined between two Android users communicating via iMessage.
At least with email it’s a bit easier to filter out spam, but iMessage is also E2E encrypted so automatic spam detection is much harder.