Assume that we have a system that sends out daily reports over email in the form of attached CSV files and that we want to access these.

function getCsvFromGmail() {
  // Get the newest Gmail thread based on sender and subject
  var gmailThread = GmailApp.search("from:[email protected] subject:\"My daily report\"", 0, 1)[0];
  
  // Get the attachments of the latest mail in the thread.
  var attachments = gmailThread.getMessages()[gmailThread.getMessageCount() - 1].getAttachments();
  
  // Get and and parse the CSV from the first attachment
  var csv = Utilities.parseCsv(attachments[0].getDataAsString());
  return csv;
}