const string str = @"
$ORIGIN example.com.     ; designates the start of this zone file in the namespace
$TTL 1h                  ; default expiration time of all resource records without their own TTL value
example.com.  IN  SOA   ns.example.com. username.example.com. ( 2007120710 1d 2h 4w 1h )
example.com.  IN  NS    ns                    ; ns.example.com is a nameserver for example.com
example.com.  IN  NS    ns.somewhere.example. ; ns.somewhere.example is a backup nameserver for example.com
example.com.  IN  MX    10 mail.example.com.  ; mail.example.com is the mailserver for example.com
@             IN  MX    20 mail2.example.com. ; equivalent to above line, ""@"" represents zone origin
@             IN  MX    50 mail3              ; equivalent to above line, but using a relative host name
example.com.  IN  A     192.0.2.1             ; IPv4 address for example.com
              IN  AAAA  2001:db8:10::1        ; IPv6 address for example.com
ns            IN  A     192.0.2.2             ; IPv4 address for ns.example.com
              IN  AAAA  2001:db8:10::2        ; IPv6 address for ns.example.com
www           IN  CNAME example.com.          ; www.example.com is an alias for example.com
wwwtest       IN  CNAME www                   ; wwwtest.example.com is another alias for www.example.com
mail          IN  A     192.0.2.3             ; IPv4 address for mail.example.com
mail2         IN  A     192.0.2.4             ; IPv4 address for mail2.example.com
mail3         IN  A     192.0.2.5             ; IPv4 address for mail3.example.com";
var zone = DnsZoneFile.Parse(content);

var zone = await DnsZoneFile.LoadAsync(uri)

var zone = new DnsZoneFile();
zone.Records.Add(new AResourceRecord {
    Name = "www.example.com",
    Class = "IN",
    Ttl = TimeSpan.FromMinutes(15),
    Address = IPAddress.Parse("127.0.0.1")
});
zone.Records.Add(new AResourceRecord {
    Name = "ftp.example.com",
    Class = "IN",
    Ttl = TimeSpan.FromMinutes(15),
    Address = IPAddress.Parse("127.0.0.1")
});
Console.Write(zone.ToString());

Console.Write(zone.ToString("example.com"));