How can I pull Salesforce objects as users, updating existing accounts when the email address matches?

The answer was to use an Event Subscriber.

Here is a generic form of my code for anyone else who may have this question. This code is working but there seems to be another event that is in the process of creating a new user which is never completed. I was getting a simple notice log that the user was not able to be created (Which is what I want); however, I would ideally be able to abort this process in the event somehow instead of letting it fail gracefully elsewhere.

Critiques and improvements are welcome!

<?php

namespace Drupal\my_module\EventSubscriber;

use Drupal\Core\StringTranslation\StringTranslationTrait;
use Drupal\salesforce\Event\SalesforceEvents;
use Drupal\salesforce_mapping\Event\SalesforcePullEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Class MyNewSubscriber.
 */
class MyNewSubscriber implements EventSubscriberInterface {

  use StringTranslationTrait;

  public function pullPrepull(SalesforcePullEvent $event) {

    /** @var \Drupal\user\Entity\User $account */
    $account = $event->getEntity();
    $mapping = $event->getMapping();
    $salesforceObj = $event->getMappedObject();

    // check if the mapping matches the one I want to revise
    switch ($mapping->id()) {
      case 'my_salesforce_mapping':
        if($account->isNew()) {
          // Be mindful that your salesforce fields may be different. Mine are "Email" and "Name"
          $sf_email = $event->getMappedObject()->getSalesforceRecord()->field('Email');
          if(empty($sf_email)) {
            $event->disallowPull(); // We will reject any salesforce records that don't have an email associated with it. You may want to do something different here
            break;
          }

          $drupal_user = user_load_by_mail($sf_email);

          // Find if a user with that email exists
          if($drupal_user != false) {
            $salesforceObj->setDrupalEntity($drupal_user);
            \Drupal::logger('salesforce')->debug("Update the user with email {$sf_email} instead of creating a duplicate");
          } else {
            \Drupal::logger('salesforce')->debug("There was an issue when updating the user - Unknown email for {$event->getMappedObject()->getSalesforceRecord()->field('Name')}");
          }
        } else {
          // I don't need to do anything because the entities are already mapped
        }
        break;
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $events = [
      SalesforceEvents::PULL_PREPULL => 'pullPrepull',
    ];
    return $events;
  }
}