public static string GetUsersEmail(string User, string UserName, string Password)
{
   string EmailAddress = "";
   DirectoryEntry Entry = new DirectoryEntry("LDAP://exchangeserver",   //Make sure to point this at your exchange server
                                               UserName,
                                               Password,
                                               AuthenticationTypes.Secure);
   DirectorySearcher Searcher = new DirectorySearcher(Entry);
   Searcher.PropertiesToLoad.Add("mail");
   string Filter = String.Format("(&(objectcategory=user)(cn=" + User + "))");

   Searcher.Filter = Filter;
   Searcher.Sort.Direction = SortDirection.Ascending;
   Searcher.Sort.PropertyName = "cn";

   SearchResultCollection Results;

   Results = Searcher.FindAll();

   foreach (SearchResult Result in Results)
   {
      ResultPropertyCollection Properties = Result.Properties;
      foreach (string Key in Properties.PropertyNames)
      {
         if (Key == "mail")
         {
            foreach (object Values in Properties[Key])
            {
               EmailAddress = Values.ToString();
            }
         }
      }
   }
   return EmailAddress;
}