static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            List<cUser> list;
            DateTime t = DateTime.Now;
            list = testProc();
            Console.Write("Результат: {0}", (DateTime.Now - t).TotalMilliseconds);
            Console.ReadKey();
            foreach (cUser i in list) { Console.Write("".PadLeft(80, '-')); Console.WriteLine(i.ToString()); }
            Console.ReadKey();
        }

        static List<cUser> testProc(string filter = "(&(objectCategory=Person)(objectClass=User))")
        {

            List<cUser> list = new List<cUser>();
            DirectoryEntry root = new DirectoryEntry();
            DirectorySearcher searcher = new DirectorySearcher(root, filter);
            searcher.Asynchronous = false;
            searcher.SizeLimit = 10000;
            searcher.PageSize = 50;
            searcher.CacheResults = true;
            SearchResultCollection result = searcher.FindAll();
            searcher.PropertiesToLoad.AddRange(new string[] { "createTimeStamp", "cn", "homePhone", "mail", "mobile", "samaccountname", "displayname", "telephoneNumber", "title", "UserAccountControl", "objectGUID", "employeeID", "lastLogonTimeStamp" });
            try
            {
                result = searcher.FindAll();
                foreach (SearchResult entry in result)
                {
                    cUser item = new cUser(entry);
                    list.Add(item);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Ошибка", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            return list;

        }
        public class cUser
        {
            private string _valueStr;
            public cUser(SearchResult data)
            {
                
                foreach (string i in new string[] { "cn", "samaccountname", "displayname", "telephoneNumber", "title", "UserAccountControl", "objectGUID", "employeeID", "lastLogonTimeStamp" })
                {
                    _valueStr += string.Format("{0}:={1}\n", i, data.Properties.Contains(i) ? data.Properties[i][0].ToString(): "null");
                }
            }
            public override string ToString()
            {
                return _valueStr;
            }
        }
    }