How to skip the next same record in the saved search?

Hi all gurus,
My script pulls the saved search of transactions. Since 1 customer may have multiple transactions (rows), when validating for customer's email, i would like the script to check only ONCE for this customer, and it should skip the next rows and exit this validation loop and go back to the saved search. 
Can this be done in 1 validation or separate for 1-customer case vs multi-customer case?

var searchResult = nlapiSearchRecord('invoice','customsearch29',null,null);  for (var i in searchResult)     var columns = searchResult[i].nlapiGetAllColumns();     var trannum = searchResult[i].getValue(columns[0]);     var customerID = searchResult[i].getValue(columns[1]);     var email = nlapiLookupField('customer', customerID, 'email');          var next_customerID = searchResult[i+1].getValue(columns[1]);         <span style="color:'"Red"'"> if (email ==null || email =='')    {          //send email to admin, 1 email only per customer       }</span>     do the other send mail