Fix: Update customer email in quote

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

@@ -0,0 +1,66 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Customer\Observer;
+
+use Magento\Framework\Event\ObserverInterface;
+use Magento\Framework\Event\Observer;
+use Magento\Framework\Exception\NoSuchEntityException;
+use Magento\Quote\Api\CartRepositoryInterface;
+
+/**
+ * Class observer UpgradeQuoteCustomerEmailObserver
+ */
+class UpgradeQuoteCustomerEmailObserver implements ObserverInterface
+{
+    /**
+     * @var CartRepositoryInterface
+     */
+    private $quoteRepository;
+
+    /**
+     * @param CartRepositoryInterface $quoteRepository
+     */
+    public function __construct(
+        CartRepositoryInterface $quoteRepository
+    ) {
+        $this->quoteRepository = $quoteRepository;
+    }
+
+    /**
+     * Upgrade quote customer email when customer has changed email
+     *
+     * @param Observer $observer
+     * @return void
+     */
+    public function execute(Observer $observer): void
+    {
+        /** @var \Magento\Customer\Model\Data\Customer $customerOrig */
+        $customerOrig = $observer->getEvent()->getOrigCustomerDataObject();
+        if (!$customerOrig) {
+            return;
+        }
+
+        $emailOrig = $customerOrig->getEmail();
+
+        /** @var \Magento\Customer\Model\Data\Customer $customer */
+        $customer = $observer->getEvent()->getCustomerDataObject();
+        $email = $customer->getEmail();
+
+        if ($email == $emailOrig) {
+            return;
+        }
+
+        try {
+            $quote = $this->quoteRepository->getForCustomer($customer->getId());
+            $quote->setCustomerEmail($email);
+            $this->quoteRepository->save($quote);
+        } catch (NoSuchEntityException $e) {
+            return;
+        }
+    }
+}

app/code/Magento/Customer/Test/Unit/Observer/UpgradeQuoteCustomerEmailObserverTest.php

@@ -0,0 +1,107 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Customer\Test\Unit\Observer;
+
+use Magento\Customer\Observer\UpgradeQuoteCustomerEmailObserver;
+
+/**
+ * Class UpgradeQuoteCustomerEmailObserverTest for testing upgrade quote customer email
+ */
+class UpgradeQuoteCustomerEmailObserverTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @var UpgradeQuoteCustomerEmailObserver
+     */
+    protected $model;
+
+    /**
+     * @var \Magento\Quote\Api\CartRepositoryInterface
+     */
+    protected $quoteRepositoryMock;
+
+    /**
+     * @var \Magento\Framework\Event\Observer
+     */
+    protected $observerMock;
+
+    /**
+     * @var \Magento\Framework\Event
+     */
+    protected $eventMock;
+
+    /**
+     * @inheritdoc
+     */
+    protected function setUp()
+    {
+        $this->observerMock = $this->getMockBuilder(\Magento\Framework\Event\Observer::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $this->eventMock = $this->getMockBuilder(\Magento\Framework\Event::class)
+            ->disableOriginalConstructor()
+            ->setMethods(['getCustomerDataObject', 'getOrigCustomerDataObject'])
+            ->getMock();
+
+        $this->observerMock->expects($this->any())->method('getEvent')->will($this->returnValue($this->eventMock));
+
+        $this->quoteRepositoryMock = $this
+            ->getMockBuilder(\Magento\Quote\Api\CartRepositoryInterface::class)
+            ->getMockForAbstractClass();
+        $this->model = new UpgradeQuoteCustomerEmailObserver($this->quoteRepositoryMock);
+    }
+
+    /**
+     * Unit test for verifying quote customers email upgrade observer
+     */
+    public function testUpgradeQuoteCustomerEmail()
+    {
+        $email = "[email protected]";
+        $origEmail = "[email protected]";
+
+        $customer = $this->getMockBuilder(\Magento\Customer\Api\Data\CustomerInterface::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+        $customerOrig = $this->getMockBuilder(\Magento\Customer\Api\Data\CustomerInterface::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $quoteMock = $this->getMockBuilder(\Magento\Quote\Model\Quote::class)
+            ->setMethods(['setCustomerEmail'])
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $this->eventMock->expects($this->any())
+            ->method('getCustomerDataObject')
+            ->will($this->returnValue($customer));
+        $this->eventMock->expects($this->any())
+            ->method('getOrigCustomerDataObject')
+            ->will($this->returnValue($customerOrig));
+
+        $customerOrig->expects($this->any())
+            ->method('getEmail')
+            ->willReturn($this->returnValue($origEmail));
+
+        $customer->expects($this->any())
+            ->method('getEmail')
+            ->willReturn($this->returnValue($email));
+
+        $this->quoteRepositoryMock->expects($this->once())
+            ->method('getForCustomer')
+            ->willReturn($quoteMock);
+
+        $quoteMock->expects($this->once())
+            ->method('setCustomerEmail');
+
+        $this->quoteRepositoryMock->expects($this->once())
+            ->method('save')
+            ->with($quoteMock);
+
+        $this->model->execute($this->observerMock);
+    }
+}

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

@@ -15,4 +15,7 @@
     <event name="sales_quote_save_after">
         <observer name="customer_visitor" instance="Magento\Customer\Observer\Visitor\BindQuoteCreateObserver" />
     </event>
+    <event name="customer_save_after_data_object">
+        <observer name="upgrade_quote_customer_email" instance="Magento\Customer\Observer\UpgradeQuoteCustomerEmailObserver"/>
+    </event>
 </config>