I have set up Postfix on an Ubuntu 18.04, with a view to sending emails from two different domains, which I will refer to here as abc.com and xyz.com. I'm trying to configure everything so that emails are not rejected. I have created the SPF record OK in the control panels for both domains, so that is not a problem.
What I'm having difficulty with is a seeming conflict between DKIM and Reverse DNS. If I set up Reverse DNS for my server to be 'mail.abc.com', I can send out mail from 'xyz.com', correctly signed with the right DKIM key, and when I check with a verification address like 'firstname.lastname@example.org', it passes the DKIM validation fine but fails an 'iprev' check because the Reverse DNS is wrong (it resolves to mail.abc.com). But when I set the from address of my 'xyz.com' mail to 'abc.com', it passes the iprev check OK, but doesn't get a DKIM signature (and potentially has a misleading From address in the email).
So is it possible to set things up on this single server so that I can send out emails from 2 different domains and have iprev and DKIM checks work OK? If so, how do I configure this?