function DNSLookupIPv4(const ADNSServer, ADomain: string): string;
var
  I: Integer;
  DNSResolver: TIdDNSResolver;
begin
  Result := '';
  DNSResolver := TIdDNSResolver.Create;
  try
    DNSResolver.Host := ADNSServer;
    DNSResolver.QueryType := [qtA];
    DNSResolver.Resolve(ADomain);
    for I := 0 to DNSResolver.QueryResult.Count - 1 do
      if DNSResolver.QueryResult[I].RecType = qtA then
      begin
        Result := (DNSResolver.QueryResult[I] as TARecord).IPAddress;
        Break;
      end;
  finally
    DNSResolver.Free;
  end;
end;

function DNSLookupIPv6(const ADNSServer, ADomain: string): string;
var
  I: Integer;
  DNSResolver: TIdDNSResolver;
begin
  Result := '';
  DNSResolver := TIdDNSResolver.Create;
  try
    DNSResolver.Host := ADNSServer;
    DNSResolver.QueryType := [qtAAAA];
    DNSResolver.Resolve(ADomain);
    for I := 0 to DNSResolver.QueryResult.Count - 1 do
      if DNSResolver.QueryResult[I].RecType = qtAAAA then
      begin
        Result := (DNSResolver.QueryResult[I] as TAAAARecord).Address;
        Break;
      end;
  finally
    DNSResolver.Free;
  end;
end;