public GABUser LookupExact(string username)
        {
            string s = username.ToLower();

            if (DataSource != null)
            {
                using (ISearch <IContactItem> search = _gab.Contacts.Search <IContactItem>())
                {
                    search.Sort("FullName", false);
                    ISearchOperator terms = search.AddOperator(SearchOperator.Or);
                    terms.AddField("urn:schemas:contacts:cn").SetOperation(SearchOperation.Like, username);
                    terms.AddField("urn:schemas:contacts:customerid").SetOperation(SearchOperation.Like, username);
                    terms.AddField("urn:schemas:contacts:email1").SetOperation(SearchOperation.Like, username);
                    using (IContactItem contact = search.SearchOne())
                    {
                        if (contact != null)
                        {
                            return(new GABUser(contact));
                        }
                    }
                }
            }

            return(new GABUser(username));
        }