Add obbserver for updating quote customer_email

Author: UncleTioma

app/code/Magento/Customer/Observer/UpgradeQuoteCustomerEmailObserver.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Magento\Customer\Observer;
+
+use Magento\Framework\Event\ObserverInterface;
+use Magento\Framework\Event\Observer;
+use Magento\Quote\Api\CartRepositoryInterface;
+
+/**
+ * Class observer UpgradeQuoteCustomerEmailObserver
+ */
+class UpgradeQuoteCustomerEmailObserver implements ObserverInterface
+{
+    /**
+     * @var CartRepositoryInterface
+     */
+    private $cartRepository;
+
+    /**
+     * @param CartRepositoryInterface $cartRepository
+     */
+    public function __construct(
+        CartRepositoryInterface $cartRepository
+    ) {
+        $this->cartRepository = $cartRepository;
+    }
+
+    /**
+     * Upgrade quote customer email when customer has changed email
+     * @param Observer $observer
+     * @return void
+     */
+    public function execute(Observer $observer)
+    {
+        /**
+         * @var \Magento\Customer\Model\Data\Customer $customer
+         */
+        $customer = $observer->getEvent()->getData('customer_data_object');
+        $email = $customer->getEmail();
+
+        /**
+         * @var \Magento\Customer\Model\Data\Customer $customer
+         */
+        $customerOrig = $observer->getEvent()->getData('orig_customer_data_object');
+        $emailOrig = $customerOrig->getEmail();
+
+        if($email != $emailOrig){
+            $quote = $this->cartRepository->getForCustomer($customer->getId());
+            $quote->setCustomerEmail($email);
+            $this->cartRepository->save($quote);
+        }
+    }
+}

app/code/Magento/Customer/etc/frontend/events.xml

@@ -29,4 +29,7 @@
         <observer name="customer_password" instance="Magento\Customer\Observer\UpgradeCustomerPasswordObserver" />
         <observer name="customer_unlock" instance="Magento\Customer\Observer\CustomerLoginSuccessObserver" />
     </event>
+    <event name="customer_save_after_data_object">
+        <observer name="upgrade_quote_customer_email" instance="Magento\Customer\Observer\UpgradeQuoteCustomerEmailObserver"/>
+    </event>
 </config>