Lambda SES bounce event handler

index.js

const AWS = require('aws-sdk');
const _ = require('lodash');

const successResponse = message => {
  return {
    statusCode: 200,
    body: JSON.stringify({
      message: message
    })
  }
};

/**
 * Deliver given message to DLQ
 *
 * @param sqs
 * @param message
 * @returns {Promise<void>}
 */
async function sendMessageToDLQ (sqs, message) {
  await sqs.sendMessage({ MessageBody: message, QueueUrl: process.env.DLQ_URL }).promise();
}

/**
 * Process bounced messages
 *
 * @param event SNS notification event
 * @return {object} Success response object
 */
exports.handler = async (event) => {
  const sns = new AWS.SNS({ region: process.env.REGION });
  const sqs = new AWS.SQS({ region: process.env.REGION });
  
  if (_.get(event, 'Records', null)) {
    for (const property in event.Records) {
      const record = event.Records[ property ];
      const notification = JSON.parse(record.Sns.Message);

      // Make sure notification type is Bounce
      if (notification.notificationType === 'Bounce') {
        const headers = _.get(notification, 'mail.headers', null);

        if (!headers) {
          // SES has a configuration error, handle failure
          await sendMessageToDLQ(sqs, record.Sns.Message);
          return successResponse('Original message headers missing');
        }

        const snsTargetArn = notification.mail.headers.find((header) => header.name === 'X-BOUNCE-SNS-TARGET-ARN');

        if (!snsTargetArn) {
          // Client did not provide the TargetArn, handle failure
          await sendMessageToDLQ(sqs, record.Sns.Message);
          return successResponse('Missing TargetArn header');
        }

        let bouncedRecipients = [];

        // Add all bounced recipients to message
        if (_.get(notification, 'bounce.bouncedRecipients', false)) {
          notification.bounce.bouncedRecipients.forEach(function (value) {
            bouncedRecipients.push({ emailAddress: value.emailAddress });
          });
        }

        // Build the message
        const message = JSON.stringify({
          messageId: notification.mail.messageId,
          bounceType: notification.bounce.bounceType,
          bounceSubType: notification.bounce.bounceSubType,
          timestamp: notification.bounce.timestamp,
          bouncedRecipients: bouncedRecipients
        });

        // Processed, publish
        await sns.publish({
          MessageAttributes: {
            'OriginalMessageId': {
              DataType: 'String',
              StringValue: bounce.messageId
            }
          },
          Subject: 'Here is a bounced email notification',
          Message: message,
          TargetArn: snsTargetArn.value
        }).promise();
      }
      else {
        // Not a bounce message. Deliver to DLQ.
        await sendMessageToDLQ(sqs, record.Sns.Message);
        return successResponse('Not a bounce message');
      }
    }
  }

  return successResponse('ok');
};