DNS server: PTR record?

Anyone here handy with DNS server installs?

I have a Synology Diskstation setup with a mail server and I have my domain hosted Domains4Less and pointing to my static IP provided by my ISP. Mail works ok but I need to create a PTR record to prevent my mail going to other peoples spam boxes. My ISP don't want to know about it. Domains4Less support have no idea what they are doing and there is a massive language barrier with their support being Indian based.. So I have decided to setup my own DNS server so I can create my own A,MX,PTR records etc. I've tried a few guides but nothing I do can get the PTR record to work.

Lets say my domain name is mydomain.nz and my static IP is: 100.20.10.1

In my domain control panel with Domains4Less I have enter 2 nameservers (ns1.mydomain.nz -> 100.20.10.1, ns2.mydomain.nz -> 100.20.10.1).

I have installed synology DNS server on my Diskstation.

In my Diskstation I have created a Master zone: Forward Zone, Domain name: mydomain.nz, Master DNS Server:192.168.1.2 (Diskstation local IP).

For the Forward zone I have created two NS records: ns1.mydomain.nz -> 100.20.10.1, ns2.mydomain.nz -> 100.20.10.1

And 1 A record: mydomain.nz -> 100.20.10.1

I have created a second Master zone: Reverse Zone, Domain name: 10.20.100.in-addr.arpa.

For the Reverse zone I have created a PTR record: 1.10.20.100.in-addr.arpa -> mydomain.nz

When I use http://mxtoolbox.com/NetworkTools.aspx to check the PTR it says no PTR record exists. Can someone please steer me in the right direction?