There wont be any custom spam protection script on
VPS Hosting. Right now your account is on a shared server and by default we need to enable RBL's in exiim configuration due to which emails coming from blacklisted sources are rejected by the server.
We wont keep those RBL's on VPs so there wont be any problem with email service and you will have full access to the exim maillogs which will allow you to see the reason for rejection even if any email gets rejected.