External Domain Zone file
From: https://www.zytrax.com/books/dns/ch6/mydomain-external.html 





DNS Sample External Domain Zone file
This file shows only hosts (services) which are externally (publicly) visible and may be used with a views 'View based Authoritative Only' server or in a 'public' server in a Stealth configuration - all internal hosts are excluded. The internal view version is here. The configuration provides:

    

  1. Two name servers are used one internal (ns1) and one external (ns2) to the domain

  2. The mail service is external to the domain (provided by a third party)

  3. FTP and WWW services are provided by the same host

  4. The host addresses are all in the class C private address range 192.168.0.0 (a slightly artificial case)



The Resource Records are all defined separately.
$TTL	86400 ; 24 hours could have been written as 24h or 1d
$ORIGIN example.com.
@  1D  IN	 SOA ns1.example.com.	hostmaster.example.com. (
			      2002022401 ; serial
			      3H ; refresh
			      15 ; retry
			      1w ; expire
			      3h ; minimum
			     )
       IN  NS     ns1.example.com. ; in the domain
       IN  NS     ns2.smokeyjoe.com. ; external to domain
       IN  MX  10 mail.another.com. ; external mail provider
; server host definitions
ns1    IN  A      192.168.0.1  ;name server definition     
www    IN  A      192.168.0.2  ;web server definition
ftp    IN  CNAME  www.example.com.  ;ftp server definition