Proper DNS configuration for email

I require support in the following: I currently have an Ubuntu server running Virtualmin with email enabled for two domains/accounts. My DNS server will be external and [login to view URL] will be hosting it. I currently do not have any SPF TXT records or proper DKIM setup (If necessary or possible) with Virtualmin so any email sent from the server goes to spam on gmail, yahoo, outlook etc. Errors seem to point improper Reverse DNS as well. I am currently working on a temporary site with [login to view URL] free dns and would appreciate instructions on how to setup everything properly on these two test websites so I can then pass on the actual websites with some support later on.