Incorrect contact creation when a susbcribed customer changes their email

[digitalpianism]

Replicated on 4.29.0

When a customer changes their email address Magento fires two events that both feed into Dotdigital via separate, independent message queues:
Flow 1 — customer_save_after event:
The CreateUpdateContact observer detects the email change and publishes a message to the ddg.email_update.queue topic

Flow 2 — newsletter_subscriber_save_after event:
When Magento core updates the subscriber record with the new email, the ChangeContactSubscription observer publishes a message to the ddg.subscription.queue topic

This causes a new contact creation and a failure in the old email contact update with the following log entries:

dotdigital.INFO: Newsletter subscribe success {"email":"newemail@address.com"} []
dotdigital.ERROR: Contact email update error: {"emailBefore":"oldemail@address.com","emailAfter":"oldemail@address.com","exception":"[object] (Dotdigital\\Exception\\ResponseValidationException(code: 500): cont...

To fix that I had to implement a custom plugin in a custom module with the following:

di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Dotdigitalgroup\Email\Observer\Newsletter\ChangeContactSubscription">
        <plugin name="vendor_dotdigitalemail_skip_subscriptions_after_email_change"
                type="Vendor\DotdigitalEmail\Plugin\Observer\Newsletter\ChangeContactSubscriptionPlugin"
                sortOrder="10" />
    </type>
</config>

ChangeContactSubscriptionPlugin.php

<?php
declare(strict_types=1);

namespace Vendor\DotdigitalEmail\Plugin\Observer\Newsletter;

use Dotdigitalgroup\Email\Logger\Logger;
use Dotdigitalgroup\Email\Observer\Newsletter\ChangeContactSubscription;
use Magento\Framework\Event\Observer;

/**
 * Skip Dotdigital subscription queue publish when a customer email change is in progress.
 *
 * When a customer changes their email address, two independent Dotdigital queue messages
 * are published from separate observers:
 *   1. ddg.contact.email_update — renames the existing contact (old email → new email)
 *   2. ddg.newsletter.subscription — syncs the subscriber with the new email
 *
 * Because these messages are consumed by separate queue consumers with no ordering
 * guarantee, the subscription consumer can run first and create a new contact with the
 * new email. When the email-update consumer then tries to rename the old contact, it
 * fails with a duplicate / validation error, leaving the old contact orphaned.
 *
 * This plugin detects the email-change scenario by comparing the subscriber's original
 * email (before save) with the current email. If they differ, it skips the observer
 * entirely, allowing the email-update consumer to handle the rename without conflict.
 * The subscriber data will be synced during the next scheduled batch sync.
 */
class ChangeContactSubscriptionPlugin
{
    /**
     * @param Logger $logger
     */
    public function __construct(
        protected Logger $logger
    ) {
    }

    /**
     * Conditionally skip the observer when a customer email change is detected.
     *
     * @param ChangeContactSubscription $subject
     * @param callable $proceed
     * @param Observer $observer
     * @return ChangeContactSubscription
     */
    public function aroundExecute(
        ChangeContactSubscription $subject,
        callable $proceed,
        Observer $observer
    ) {
        $subscriber = $observer->getEvent()->getSubscriber();
        $origEmail = $subscriber->getOrigData('subscriber_email');
        $currentEmail = $subscriber->getEmail();

        if ($origEmail && $origEmail !== $currentEmail) {
            $this->logger->info(
                'Vendor_DotdigitalEmail: Skipping ChangeContactSubscription observer — '
                . 'email change in progress, deferring to email-update consumer',
                [
                    'emailBefore' => $origEmail,
                    'emailAfter' => $currentEmail,
                ]
            );

            return $subject;
        }

        return $proceed($observer);
    }
}