C#查询DNS的MX地址的代码

//C#查询DNS的MX地址的代码namespace PAB.DnsUtils { using System; using System.Collections; using System.ComponentModel; using System.Runtime.InteropServices;  public class DnsMx {  public DnsMx()  {  }    [DllImport("dnsapi", EntryPoint="DnsQuery_W", CharSet=CharSet.Unicode, SetLastError=true, ExactSpelling=true)]  private static extern int DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)]ref string pszName, QueryTypes wType, QueryOptions options, int aipServers, ref IntPtr ppQueryResults, int pReserved);    [DllImport("dnsapi", CharSet=CharSet.Auto, SetLastError=true)]  private static extern void DnsRecordListFree(IntPtr pRecordList, int FreeType);    public static string[] GetMXRecords(string domain)   {    IntPtr ptr1=IntPtr.Zero ;   IntPtr ptr2=IntPtr.Zero ;   MXRecord recMx;      if (Environment.OSVersion.Platform != PlatformID.Win32NT)   {     throw new NotSupportedException();   }       ArrayList list1 = new ArrayList();      int num1 = DnsMx.DnsQuery(ref domain, QueryTypes.DNS_TYPE_MX, QueryOptions.DNS_QUERY_BYPASS_CACHE, 0, ref ptr1, 0);      if (num1 != 0) { throw new Win32Exception(num1); }      for (ptr2 = ptr1; !ptr2.Equals(IntPtr.Zero); ptr2 = recMx.pNext)   {    recMx = ( MXRecord) Marshal.PtrToStructure(ptr2, typeof(MXRecord));        if (recMx.wType == 15)    {      string text1 = Marshal.PtrToStringAuto(recMx.pNameExchange);     list1.Add(text1);    }   }      DnsMx.DnsRecordListFree(ptr2, 0);      return (string[]) list1.ToArray(typeof(string));  }    private enum QueryOptions { DNS_QUERY_ACCEPT_TRUNCATED_RESPONSE = 1, DNS_QUERY_BYPASS_CACHE = 8, DNS_QUERY_DONT_RESET_TTL_VALUES = 0x100000, DNS_QUERY_NO_HOSTS_FILE = 0x40, DNS_QUERY_NO_LOCAL_NAME = 0x20, DNS_QUERY_NO_NETBT = 0x80, DNS_QUERY_NO_RECURSION = 4, DNS_QUERY_NO_WIRE_QUERY = 0x10, DNS_QUERY_RESERVED = -16777216, DNS_QUERY_RETURN_MESSAGE = 0x200, DNS_QUERY_STANDARD = 0, DNS_QUERY_TREAT_AS_FQDN = 0x1000, DNS_QUERY_USE_TCP_ONLY = 2, DNS_QUERY_WIRE_ONLY = 0x100 }    private enum QueryTypes { DNS_TYPE_MX = 15 }    [StructLayout(LayoutKind.Sequential)]  private struct MXRecord   {   public IntPtr pNext;   public string pName;   public short wType;   public short wDataLength;   public int flags;   public int dwTtl;   public int dwReserved;   public IntPtr pNameExchange;   public short wPreference;   public short Pad;  } } }static void Main(string[] args) { string[] s= PAB.DnsUtils.DnsMx.GetMXRecords("microsoft.com");  foreach (string st in s) Console.WriteLine("Server: {0}",st);  Console.ReadLine();}