Can you split a domains email between SPAMCuda and somewhere else?
The short answer is no. The reason is that MX records in the DNS do not allow mailbox names to be associated with them, so there is no way to specify that email to “admin” should go to one place while email to “user1”, both on the same domain, should go to a different machine. As such if you point a domain at SPAMCuda, then all email for that domain must be received and processed here.