Retuning a GMail script to prevent "Exceeded maximum execution time" - google-apps-script

Question

I use a gmail account to receive status updates from devices which I have listed in a Google spreadsheet by its user and serial number. The status update email will have the serial number of the device in it's email subject and will usually be sent about once a week per device. Due to the number of devices (600+), I get a pretty constant influx of status updates from various devices every day. What I'm trying to do is setup a script that will search my Inbox and create a list of devices that I haven't received a status update email from which would prompt me to figure out why that device isn't reporting in.
I've modified a script I found online at: http://forums.mozillazine.org/viewtopic.php?f=46&t=2740775. It works by obtaining a device serial number listed in a spreadsheet and searching the Inbox for an email subject with that serial number sent within the past 15 days. The script works fine when the spreadsheet has about 200 items, but beyond that I start getting an "Exceeded maximum execution time" error and I need it to do 600+ items now and more as time goes on. I also had to add the Utilities.sleep(1000) line to avoid a "Service invoked too many times in a short time: gmail rateMax" error. Is there a better way to write this script to avoid these errors?
function SearchEmail() {
var sheet = SpreadsheetApp.getActiveSheet();
var data = sheet.getDataRange().getValues();
var waittime = 15;
var emailTo = "temp#email.com";
var emailSubject = "NO EMAIL IN " + waittime + " DAYS FROM FOLLOWING DEVICES";
var emailText = "";
for (var i = 1; i < data.length; i++) {
Utilities.sleep(1000);
var j = i + 1;
var gsearch = "in:inbox subject:(" + data[i][1] + ") newer_than:" + waittime + "d";
var threads = GmailApp.search(gsearch, 0, 1);
if (threads.length == 0) {
var emailText = emailText + j + " Device: " + data[i][1] + " User: " + data[i][0] + "\n";
}
}
MailApp.sendEmail(emailTo, emailSubject, emailText);
}

Answer 1

I'd suggest you see the problem from another point of view.
Could you find a common string to all the emails that your report is sending ? Something like "device status" in the subject or in the body...
This way you could search your inbox for that string, put a label on it so that you avoid rechecking them and use a simple function to check in your spreadsheet if that number is in the list.
function checkList(device){
var sheet = SpreadsheetApp.getActiveSheet();
var data = sheet.getDataRange().getValues();
for(var n=0;n<data.length;n++){
if(data[n][0]==device){ return true};// assuming number are in column A
}
return false;
}
then send a mail only if(checkList(device)!=true){
This would be far more efficient I think.