Mail Channels has been mentioned but by the system only working with pre-defined systems, this limits what can be done.
We use our own in-house system where cPanel currently adds domains via hooks, sets the correct MX records and then tears that down when the domain is deleted. It works perfectly.
Enhance needs a hooks system to allow this to be possible but also the ability to add intermediate MXs as trusted so that no SPF or DKIM checks are done on the receiving server (similar to cPanel backup MX).
Finally, there needs to be a way that we can implement our own modules for Enhance so that custom filtering options for our spam solution can appear as native options against a users domain (and the ability to remove the spam level options built in to Enhance).