You can look up the daily limits here.

Regarding your code, looking at the execution transcript it looks like the script isn't recognizing row as an integer but as a string, it attaches the 2 and only then converts it. So you're deleting row 2 (or 02), then row 12, then row 22 and so on.

This however is irrelevant because there's a problem in your logic. I'll try my best to explain it and hope that it is understandable.

If you delete a row after every iteration, then in the first iteration it would delete row 2 (because row = 0 and you add 2), in the second iteration it would delete row 3 (because row = 1 and you add 2), but since in your first iteration you already deleted a row the data that was in row 3 at the beginning is now actually in row 2.

One way to tackle this problem is by reversing the loop, start at the max and count down. This way when you delete a row it has no effect on the next one. I've rewritten your code a bit, so that it should work like intended.

function sendEmails() {

  var ss = SpreadsheetApp.getActiveSpreadsheet();

  var sheet = ss.getSheets()[0];

  var startRow = 2;  // First row of data to process

  var lastRow = sheet.getLastRow(); // getLastRow() gives you the last row that has content, while getMaxRows gives you the maximum number of rows in your sheet

  var range = sheet.getRange(startRow, 1, lastRow-1, 50)  // -1 because you want the number of rows from your starting position and not the index of the last row

  var values = range.getValues();



 for (row = values.length-1; row >= 0; row--) { 

     var theID = values[row][0];

     var message = ;

     var sendto = ;

     var emailAddress = values[row][2];

     if (emailAddress==Autre){[email protected]}

     if (emailAddress==Autre1){[email protected]}

     if (emailAddress==Autre2){[email protected]}

    message+=n ID:  + values[row][1];

    message+=n Project Number:  + values[row][2];



    var subject = Project ID:  + values[row][1];



   if (sendto!=''){

     MailApp.sendEmail(sendto, subject, message);

     sheet.deleteRow(row+2)

    }

 }

}

I hope this is somewhat understandable, I'm not very good at explaining things.