dns-lookup | Here 's where to use these tools | DNS library

I have a couple of web sites and an hmailserver on my VPS. I recently noticed that comcast, and I guess others, are rejecting email where there is no PTR or rDNS. I can set up the PTR in DNS but not sure about the rDNS. I came across an old blog that shows how to do it in older versions of IIS but I'm not sure if this is the right way or how to do it in IIS-10

Say I have 3 domains myDomain1.com and MyDomain2.com both use Ip x.x.x.y and myMailServer.com uses Ip x.x.x.z

DNS for these are all set up on cloudflare. MX records for the MyDomain1 and MyDomain2 both point to mail.MyMailserver.com. I use hmailserver and all this works fine.

Comcast says I need a PTR record which I can set up on Cloudflare, and rDNS which is what I'm asking about.

This blog

http://www.expta.com/2010/01/how-to-enable-reverse-dns-lookup-in-iis.html

shows how to do it in earlier versions of IIS (I am on IIS-10) using IP Address and Domain Restrictions

So my questions are :

1 - if this is not the right way then please redirect me! else
2 - Do I use Allow Entry or Deny Entry?
3 - Do I use the mail domain x.x.x.z for all or the ip assigned in DNS - or both?
4 - do I do this for all domains?

Thanks