Google Apps Script that searches for "undeliverable" emails and extracts email addresses that bounced. Pastes emails and context into Google Sheet for analysis.

UndeliverableEmailExtractor.js

function processInboxToSheet() {
  var threads = GmailApp.search("Undeliverable", 0, 500)
  //Replace ID with one of your private spreadsheets ID
  var sheet = SpreadsheetApp.openById("16RsL_4fh0WXSICw5VJDHVAKtija21JBxxxxxxxxx").getActiveSheet();
  for (var i = 0; i < threads.length; i++) {
    var messages = threads[i].getMessages();
    for (var j = 0; j < messages.length; j++){
      var subject = messages[j].getSubject();
      var content = messages[j].getPlainBody();
      var date = messages[j].getDate();
      if (RegExp(/Original Message Headers/i).test(content)){
        var extract = content.match(RegExp(/[\s\S]*?(?=Original Message Headers)/i)).toString();
        var email = extract.match(/[^\s\:\(\)\,\<\>\@]+@[^\s\:\(\)\,\<\>\@]+/g);
        var type = extract.match(/Policy violation or system error|Invalid recipient|Quota|Hop count exceeded|Connection refused|mailbox full|SPF validation error|554 delivery error|mailbox is disabled|doesn't have|spam|mailbox unavailable|Message expired|user|wasn't found|does not exist|RecipNotFound|DNS|overquota|expired|Unknown to address|Spam or virus detected/gi);
        type ? type=type.toString() : type="none";
        if(!email) Logger.log(extract);
        else{
          for (var k = 0; k < email.length; k++){
            if(email.indexOf(email[k])>=k){
              sheet.appendRow([date,subject, email[k],type]);
            }
          }
        }
      }
    }
  }
}

This is a similar snippet developed by the prolific add-on developer Amit Agarwal which works for bounce messages sent directly by Gmail (I send emails through Outlook via alias so my code is slightly different). His is definitely cleaner - but basically the same.
https://www.labnol.org/code/20297-gmail-parse-bounced-emails

function getBouncedEmails() {

    /* Written by Amit Agarwal */
    /* Email: [email protected]  */

    // Write the bounced email report to a Google SpreadsheetApp
    var sheet = SpreadsheetApp.getActiveSheet();
    sheet.getRange(2, 1, sheet.getLastRow(), sheet.getLastColumn()).clearContent();

    // Find all emails returned via Gmail Mailer Maemon
    var query = "from:([email protected] OR [email protected])";

    // Get the most recent 500 bounced email messages in Gmail
    GmailApp.search(query, 0, 500).forEach(function(thread) {
        thread.getMessages().forEach(function(message) {
            if (message.getFrom().indexOf("mailer-daemon") !== -1) {
                var body = message.getPlainBody();
                // Get the bounced email address from the body
                var matches = body.match(/Delivery to[\s\S]+?(\S+\@\S+)\s([\s\S]+?)----- Original Message/);
                if (matches) {
                    // Get the exact reason for the email bounce
                    var reason = matches[2].match(/The error.+:\s+(.+)/) || matches[2].match(/Technical details.+:\s+(.+)/);
                    if (reason) {
                        // Save the data in a Google Spreadsheet
                        sheet.appendRow([
                            thread.getLastMessageDate(),
                            matches[1],
                            reason[1].replace(/ (Please|Learn|See).*$/, ""),
                            thread.getPermalink(),
                            thread.getFirstMessageSubject()
                        ]);
                    }
                }
            }
        });
    });
}