Setup wizard, new install, hostname, working email, rDNS

Hi, doing new install. My vps got 1 IP and 1 ipv4 rDNS entry and 1 ipv6 rDNS in panel.

I got 2 domain names, I am aware I can set only 1 with proper email service and other one will be going to spam.

my main domain is

and I want email [email protected]

When I installed Ubuntu 20.04 I set hostname as (that was old method used to work I think)

But i had emails not going to gmail etc, and bit confused so doing fresh install.

My question is, what hostname to use and rDNS to get [email protected]

What I put in wizard in cyberpanel as hostname and what rDNS should I set, atm its, but when I put in wizard it says they dont match.

Can You let me know what hostname should I set in wizard and what rDNS to get website and email [email protected] please.