1200 emails per hour is only 20 emails per minute; not a lot at all. You haven't told us anything about your business model so I can't even begin to suggest why you might or might not need multiple IP#s.
DirectAdmin uses exim as it's email server and has a highly customized exim.conf configuration file, but you can certainly modify it further, or pay someone else to modify it further, to fit your needs.
Jeff