Get SIP address from active directory

The below code will be used to get the SIP address from the active directory. SIP address is commonly used in office communicator server. I have used this code to fetch the SIP address. Based on the SIP address, we have applied provisioning on office communicator server 2007.

private string GetSIPAddress(string email)
       {
           DirectoryEntry directoryEntry =
                    new DirectoryEntry(ConfigurationManager.AppSettings["LDAPPATH"]);

           string resultValue = "";

           using (HostingEnvironment.Impersonate())
           {
               DirectorySearcher directorySearcher = new DirectorySearcher(directoryEntry);
               directorySearcher.Filter = string.Format("(&(objectClass=user)(objectCategory=user) (mail={0}))", email);

               directorySearcher.PropertiesToLoad.Add("msRTCSIP-PrimaryUserAddress");

               SearchResult result = directorySearcher.FindOne();

               if (result != null)
               {
                   if (result.Properties["msRTCSIP-PrimaryUserAddress"] != null)
                   {
                       resultValue = result.Properties["msRTCSIP-PrimaryUserAddress"][0].ToString();
                       resultValue = "'" + resultValue + "'";
                   }
               }
           };
           return resultValue;
       }