Am I supposed to change "25612-21212.vps.digitalpacific.com.au" to "server1.mydomain.com"
"25612-21212" to "server1" for hostname or just leave that..?
As stated above, don't fiddle with your network configuration
. Nothing you need to do as related to ISPConfig requires you to change the default networking setup.
Don't add the IPv6 bit, either. Unless your hosting provider has assigned an IPv6 address to you, and your DNS server (I should say, your hosting provider's DNS server) is IPv6-capable, doing so only invites trouble.
The hostname that your provider has assigned to your VPS should not be changed. This ensures that your server is always reachable
at that hostname, even if your "primary domain" (e.g., urbancampsite.com) is unresponsive. Maybe you let your domain name registration expire, maybe someone hacks your registration... there are a number of reasons for which you should not change anything related to that pre-assigned hostname.
The are only a couple of exceptions:
1.) your Postfix configuration files, in that the myhostname
directive may be set to any domain that resolves to your IP address (e.g., urbancampsite.com), but
2.) if you make that change, you should ensure that your rDNS (reverse DNS) lookup matches -- that is, an rDNS against your IP address resolves to urbancampsite.com; this is usually done by setting the "primary domain" within the hosting provider's interface (e.g., to urbancampsite.com), and ensuring that the PTR (reverse DNS) record is accurate.