Receive emails from specific IP only

Hello Community! I am seeking for help to make/configure the following thing - we have external spam filtering system, which is used only by several customers, not all. Is there a way to set, so that those domains would only receive emails if they are coming from spamfilter's IP address? Otherwise spammers deliver emails directly to server, regardless MX record in DNS. Is it possible to configure? :) Regards, Anton