onEdit(event).gs

function onEdit(event)
{
  var timezone = "UTC+!NUMBER";
  var timestamp_format = "EEEE dd MMMM yyyy hh:mm:ss"; //Custom date format
  var updateColName = "post-sent"; // Responder
  var timeStampColName = "post-receive"; // Output
  var sheet = event.source.getSheetByName('!SHEETNAME');


  var actRng = event.source.getActiveRange();
  var editColumn = actRng.getColumn();
  var index = actRng.getRowIndex();
  var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues();
  var dateCol = headers[0].indexOf(timeStampColName);
  var updateCol = headers[0].indexOf(updateColName); updateCol = updateCol+1;
  if (dateCol > -1 && index > 1 && editColumn == updateCol) {
    var cell = sheet.getRange(index, dateCol + 1);
    var date = Utilities.formatDate(new Date(), timezone, timestamp_format);
    cell.setValue(date);
  }
}