Another key value to review is the TTL, which Microsoft configured for every two hours. TTL represents the time that a name server is allowed to cache data. Once the time expires, the server must get new data from the authoritative servers. A short TTL is useful because it keeps the information consistent but at the expense of performance on the network and server.
To learn more about DNS configuration, the best book around is DNS and BIND from the O'Reilly Nutshell series.