diff --git a/CHANGELOG.md b/CHANGELOG.md
index 65846a0854..06336a357b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## 4.3.0 - Unreleased
 
 - Guest customers registering during checkout now have their addresses saved to their account.
+- Deprecated `craft\commerce\elements\Order::setEmail()`. `Order::setCustomer()` should be used instead.
 
 ## Unreleased
 
diff --git a/src/controllers/CartController.php b/src/controllers/CartController.php
index 61af99d9bd..e2836ad29c 100644
--- a/src/controllers/CartController.php
+++ b/src/controllers/CartController.php
@@ -221,7 +221,8 @@ public function actionUpdateCart(): ?Response
             $email = $this->request->getParam('email');
             if ($email && ($this->_cart->getEmail() === null || $this->_cart->getEmail() != $email)) {
                 try {
-                    $this->_cart->setEmail($email);
+                    $user = Craft::$app->getUsers()->ensureUserByEmail($email);
+                    $this->_cart->setCustomer($user);
                 } catch (\Exception $e) {
                     $this->_cart->addError('email', $e->getMessage());
                 }
diff --git a/src/elements/Order.php b/src/elements/Order.php
index a38c40a3b8..1bf2b6b9ca 100644
--- a/src/elements/Order.php
+++ b/src/elements/Order.php
@@ -1138,20 +1138,6 @@ class Order extends Element
      */
     private ?string $_paymentCurrency = null;
 
-    /**
-     * @var string|null
-     * @see Order::setEmail() To set the order email
-     * @see Order::getEmail() To get the email
-     * ---
-     * ```php
-     * echo $order->email;
-     * ```
-     * ```twig
-     * {{ order.email }}
-     * ```
-     */
-    private ?string $_email = null;
-
     /**
      * @var Transaction[]|null
      * @see Order::getTransactions()
@@ -1177,7 +1163,7 @@ class Order extends Element
      * {{ order.customer }}
      * ```
      */
-    private User|null|false $_customer;
+    private User|null|false $_customer = null;
 
     /**
      * @var float|null
@@ -1356,7 +1342,6 @@ public function attributes(): array
         $names[] = 'customerId';
         $names[] = 'paymentCurrency';
         $names[] = 'paymentAmount';
-        $names[] = 'email';
         $names[] = 'isPaid';
         $names[] = 'itemSubtotal';
         $names[] = 'itemTotal';
@@ -1440,6 +1425,7 @@ public function fields(): array
             };
         }
 
+        $fields['email'] = 'email';
         $fields['paidStatusHtml'] = 'paidStatusHtml';
         $fields['customerLinkHtml'] = 'customerLinkHtml';
         $fields['orderStatusHtml'] = 'orderStatusHtml';
@@ -1511,7 +1497,6 @@ protected function defineRules(): array
 
             [['paymentSourceId'], 'number', 'integerOnly' => true],
             [['paymentSourceId'], 'validatePaymentSourceId'],
-            [['email'], 'email'],
 
             [['number', 'user', 'orderCompletedEmail', 'saveBillingAddressOnOrderComplete', 'saveShippingAddressOnOrderComplete'], 'safe'],
         ]);
@@ -2312,10 +2297,6 @@ public function getCustomer(): ?User
             }
         }
 
-        if ($this->_customer) {
-            $this->_email = $this->_customer->email;
-        }
-
         return $this->_customer ?: null;
     }
 
@@ -2329,7 +2310,8 @@ public function setCustomer(?User $customer = null): void
         $this->_customer = $customer;
         if ($this->_customer) {
             $this->_customerId = $this->_customer->id;
-            $this->_email = $this->_customer->email;
+        } else {
+            $this->_customerId = null;
         }
     }
 
@@ -2338,7 +2320,7 @@ public function setCustomer(?User $customer = null): void
      */
     public function getUser(): ?User
     {
-        Craft::$app->getDeprecator()->log('Order::getUser()', 'The `Order::getUser()` is deprecated, use the `Order::getCustomer()` instead.');
+        Craft::$app->getDeprecator()->log('Order::getUser()', 'The `Order::getUser()` is deprecated, use `Order::getCustomer()` instead.');
         return $this->getCustomer();
     }
 
@@ -2347,37 +2329,37 @@ public function getUser(): ?User
      *
      * @param string|null $email
      * @throws Exception
+     * @deprecated in 4.3.0. Use [[setCustomer()]] instead.
      */
     public function setEmail(?string $email): void
     {
+        Craft::$app->getDeprecator()->log(__METHOD__, '`Order::setEmail()` has been deprecated use `Order::setCustomer()` instead.');
         if (!$email) {
             $this->_customer = null;
             $this->_customerId = null;
-            $this->_email = null;
             return;
         }
 
-        if ($this->_email === $email) {
+        if ($this->_customer && $this->_customer->email === $email) {
             return;
         }
 
         $user = Craft::$app->getUsers()->ensureUserByEmail($email);
-        $this->_email = $email;
         $this->setCustomer($user);
     }
 
     /**
-     * Returns the email for this order. Will always be the registered users email if the order's customer is related to a user.
+     * Returns the email for this order. Will always be the customer's email if they exist.
+     * @return string|null
      */
     public function getEmail(): ?string
     {
-        if ($user = $this->getCustomer()) {
-            $this->_email = $user->email;
-        }
-
-        return $this->_email ?? null;
+        return $this->getCustomer()?->email ?? null;
     }
 
+    /**
+     * @return bool
+     */
     public function getIsPaid(): bool
     {
         return !$this->hasOutstandingBalance() && $this->isCompleted;
diff --git a/src/elements/db/OrderQuery.php b/src/elements/db/OrderQuery.php
index 49eacced74..9b03a170c0 100644
--- a/src/elements/db/OrderQuery.php
+++ b/src/elements/db/OrderQuery.php
@@ -1412,6 +1412,14 @@ public function withTransactions(bool $value = true): OrderQuery
      */
     public function populate($rows): array
     {
+        // @TODO remove at next breaking change
+        // Remove `email` key from each row.
+        array_walk($rows, function(&$row) {
+            if (array_key_exists('email', $row)) {
+                unset($row['email']);
+            }
+        });
+
         /** @var Order[] $orders */
         $orders = parent::populate($rows);
 
@@ -1463,7 +1471,10 @@ protected function beforePrepare(): bool
             'commerce_orders.couponCode',
             'commerce_orders.orderStatusId',
             'commerce_orders.dateOrdered',
+
+            // @TODO remove at next breaking change
             'commerce_orders.email',
+
             'commerce_orders.isCompleted',
             'commerce_orders.datePaid',
             'commerce_orders.currency',
@@ -1538,7 +1549,9 @@ protected function beforePrepare(): bool
         }
 
         if (isset($this->email) && $this->email) {
-            $this->subQuery->andWhere(Db::parseParam('commerce_orders.email', $this->email, '=', true));
+            // Join and search the users table for email address
+            $this->subQuery->leftJoin(CraftTable::USERS . ' users', '[[users.id]] = [[commerce_orders.customerId]]');
+            $this->subQuery->andWhere(Db::parseParam('users.email', $this->email, '=', true));
         }
 
         // Allow true ot false but not null
diff --git a/src/services/Carts.php b/src/services/Carts.php
index f055185c2c..6a5f763582 100644
--- a/src/services/Carts.php
+++ b/src/services/Carts.php
@@ -153,10 +153,9 @@ public function getCart(bool $forceSave = false): Order
         $this->_cart->paymentCurrency = $this->_getCartPaymentCurrencyIso();
         $this->_cart->origin = Order::ORIGIN_WEB;
 
-        if ($currentUser) {
-            if ($this->_cart->getCustomer() === null || ($currentUser->email && $currentUser->email !== $this->_cart->email)) {
-                $this->_cart->setEmail($currentUser->email); // Will ensure the customer is also set
-            }
+        // Switch the cart customer if needed
+        if ($currentUser && ($this->_cart->getCustomer() === null || ($currentUser->email && $currentUser->email !== $this->_cart->getEmail()))) {
+            $this->_cart->setCustomer($currentUser);
         }
 
         $hasIpChanged = $originalIp != $this->_cart->lastIp;
diff --git a/src/services/Customers.php b/src/services/Customers.php
index 4459d805fa..ee13c74797 100644
--- a/src/services/Customers.php
+++ b/src/services/Customers.php
@@ -380,75 +380,72 @@ private function _saveAddressesFromOrder(Order $order): void
      */
     private function _activateUserFromOrder(Order $order): void
     {
-        if (!$order->email) {
+        $user = $order->getCustomer();
+        if (!$user || $user->getIsCredentialed()) {
             return;
         }
 
-        $user = Craft::$app->getUsers()->ensureUserByEmail($order->email);
+        $billingAddress = $order->getBillingAddress();
+        $shippingAddress = $order->getShippingAddress();
 
-        if (!$user->getIsCredentialed()) {
-            $billingAddress = $order->getBillingAddress();
-            $shippingAddress = $order->getShippingAddress();
-
-            if (!$user->fullName) {
-                $user->fullName = $billingAddress?->fullName ?? $shippingAddress?->fullName ?? '';
-            }
+        if (!$user->fullName) {
+            $user->fullName = $billingAddress?->fullName ?? $shippingAddress?->fullName ?? '';
+        }
 
-            $user->username = $order->email;
-            $user->pending = true;
-            $user->setScenario(Element::SCENARIO_ESSENTIALS);
+        $user->username = $order->getEmail();
+        $user->pending = true;
+        $user->setScenario(Element::SCENARIO_ESSENTIALS);
 
-            if (Craft::$app->getElements()->saveElement($user)) {
-                Craft::$app->getUsers()->assignUserToDefaultGroup($user);
-                $emailSent = Craft::$app->getUsers()->sendActivationEmail($user);
+        if (Craft::$app->getElements()->saveElement($user)) {
+            Craft::$app->getUsers()->assignUserToDefaultGroup($user);
+            $emailSent = Craft::$app->getUsers()->sendActivationEmail($user);
 
-                if (!$emailSent) {
-                    Craft::warning('"registerUserOnOrderComplete" used to create the user, but couldn’t send an activation email. Check your email settings.', __METHOD__);
-                }
+            if (!$emailSent) {
+                Craft::warning('"registerUserOnOrderComplete" used to create the user, but couldn’t send an activation email. Check your email settings.', __METHOD__);
+            }
 
-                if ($billingAddress || $shippingAddress) {
-                    $newAttributes = ['ownerId' => $user->id];
+            if ($billingAddress || $shippingAddress) {
+                $newAttributes = ['ownerId' => $user->id];
 
-                    // If there is only one address make sure we don't add duplicates to the user
-                    if ($order->hasMatchingAddresses()) {
-                        $newAttributes['title'] = Craft::t('commerce', 'Address');
-                        $shippingAddress = null;
-                    }
+                // If there is only one address make sure we don't add duplicates to the user
+                if ($order->hasMatchingAddresses()) {
+                    $newAttributes['title'] = Craft::t('commerce', 'Address');
+                    $shippingAddress = null;
+                }
 
-                    // Copy addresses to user
-                    if ($billingAddress) {
-                        $newBillingAddress = Craft::$app->getElements()->duplicateElement($billingAddress, $newAttributes);
+                // Copy addresses to user
+                if ($billingAddress) {
+                    $newBillingAddress = Craft::$app->getElements()->duplicateElement($billingAddress, $newAttributes);
 
-                        /**
-                         * Because we are cloning from an order address the `CustomerAddressBehavior` hasn't been instantiated
-                         * therefore we are unable to simply set the `isPrimaryBilling` property when specifying the new attributes during duplication.
-                         */
-                        if (!$newBillingAddress->hasErrors()) {
-                            $this->savePrimaryBillingAddressId($user, $newBillingAddress->id);
+                    /**
+                     * Because we are cloning from an order address the `CustomerAddressBehavior` hasn't been instantiated
+                     * therefore we are unable to simply set the `isPrimaryBilling` property when specifying the new attributes during duplication.
+                     */
+                    if (!$newBillingAddress->hasErrors()) {
+                        $this->savePrimaryBillingAddressId($user, $newBillingAddress->id);
 
-                            if ($order->hasMatchingAddresses()) {
-                                $this->savePrimaryShippingAddressId($user, $newBillingAddress->id);
-                            }
+                        if ($order->hasMatchingAddresses()) {
+                            $this->savePrimaryShippingAddressId($user, $newBillingAddress->id);
                         }
                     }
+                }
 
-                    if ($shippingAddress) {
-                        $newShippingAddress = Craft::$app->getElements()->duplicateElement($shippingAddress, $newAttributes);
+                if ($shippingAddress) {
+                    $newShippingAddress = Craft::$app->getElements()->duplicateElement($shippingAddress, $newAttributes);
 
-                        /**
-                         * Because we are cloning from an order address the `CustomerAddressBehavior` hasn't been instantiated
-                         * therefore we are unable to simply set the `isPrimaryShipping` property when specifying the new attributes during duplication.
-                         */
-                        if (!$newShippingAddress->hasErrors()) {
-                            $this->savePrimaryShippingAddressId($user, $newShippingAddress->id);
-                        }
+                    /**
+                     * Because we are cloning from an order address the `CustomerAddressBehavior` hasn't been instantiated
+                     * therefore we are unable to simply set the `isPrimaryShipping` property when specifying the new attributes during duplication.
+                     */
+                    if (!$newShippingAddress->hasErrors()) {
+                        $this->savePrimaryShippingAddressId($user, $newShippingAddress->id);
                     }
                 }
-            } else {
-                $errors = $user->getErrors();
-                Craft::warning('Could not create user on order completion.', __METHOD__);
-                Craft::warning($errors, __METHOD__);
             }
+        } else {
+            $errors = $user->getErrors();
+            Craft::warning('Could not create user on order completion.', __METHOD__);
+            Craft::warning($errors, __METHOD__);
         }
     }
 }
diff --git a/tests/unit/elements/order/OrderCustomerTest.php b/tests/unit/elements/order/OrderCustomerTest.php
new file mode 100644
index 0000000000..8404d5030f
--- /dev/null
+++ b/tests/unit/elements/order/OrderCustomerTest.php
@@ -0,0 +1,112 @@
+<?php
+/**
+ * @link https://craftcms.com/
+ * @copyright Copyright (c) Pixel & Tonic, Inc.
+ * @license https://craftcms.github.io/license/
+ */
+
+namespace unit\elements\order;
+
+use Codeception\Test\Unit;
+use craft\commerce\elements\Order;
+use craft\services\Deprecator;
+use craftcommercetests\fixtures\OrdersFixture;
+use UnitTester;
+use yii\base\Exception;
+use yii\base\InvalidConfigException;
+
+/**
+ * OrderCustomerTest
+ *
+ * @author Pixel & Tonic, Inc. <support@pixelandtonic.com>
+ * @since 4.3.0
+ */
+class OrderCustomerTest extends Unit
+{
+    /**
+     * @var UnitTester
+     */
+    protected $tester;
+
+    /**
+     * @return array
+     */
+    public function _fixtures(): array
+    {
+        return [
+            'orders' => [
+                'class' => OrdersFixture::class,
+            ],
+        ];
+    }
+
+    /**
+     * @param string $email
+     * @return void
+     * @throws Exception
+     * @throws InvalidConfigException
+     * @dataProvider emailDataProvider
+     */
+    public function testSetEmail(string $email): void
+    {
+        \Craft::$app->set('deprecator', $this->make(Deprecator::class, [
+            'log' => function(string $key, string $message, ?string $file = null, ?int $line = null) {
+                self::once();
+                self::assertEquals(Order::class . '::setEmail', $key);
+            },
+        ]));
+
+        $order = new Order();
+        $order->setEmail($email);
+
+        self::assertEquals($email, $order->getEmail());
+        self::assertNotNull($order->getCustomer());
+        self::assertEquals($email, $order->getCustomer()->email);
+    }
+
+    /**
+     * @return array[]
+     */
+    public function emailDataProvider(): array
+    {
+        return [
+            'existing-credentialed-user' => ['email' => 'customer1@crafttest.com'],
+            'existing-inactive-user' => ['email' => 'inactive.user@crafttest.com'],
+        ];
+    }
+
+    /**
+     * @param string $email
+     * @return void
+     * @dataProvider customerDataProvider
+     */
+    public function testSetCustomer(string $email): void
+    {
+        $user = \Craft::$app->getUsers()->getUserByUsernameOrEmail($email);
+        $order = new Order();
+        $order->setCustomer($user);
+
+        self::assertEquals($email, $order->getEmail());
+        self::assertNotNull($order->getCustomer());
+        self::assertEquals($email, $order->getCustomer()->email);
+        self::assertEquals($user->id, $order->getCustomer()->id);
+        self::assertEquals($user->id, $order->getCustomerId());
+
+        // Test remove customer
+        $order->setCustomer();
+        self::assertNull($order->getCustomer());
+        self::assertNull($order->getCustomerId());
+        self::assertNull($order->getEmail());
+    }
+
+    /**
+     * @return array[]
+     */
+    public function customerDataProvider(): array
+    {
+        return [
+            'existing-credentialed-user' => ['email' => 'customer1@crafttest.com'],
+            'existing-inactive-user' => ['email' => 'inactive.user@crafttest.com'],
+        ];
+    }
+}
diff --git a/tests/unit/elements/order/OrderMarkAsCompleteTest.php b/tests/unit/elements/order/OrderMarkAsCompleteTest.php
index 76c3b0f805..60a3e9a6da 100644
--- a/tests/unit/elements/order/OrderMarkAsCompleteTest.php
+++ b/tests/unit/elements/order/OrderMarkAsCompleteTest.php
@@ -60,7 +60,8 @@ public function testUpdatedProperties(): void
     {
         $order = new Order();
         $email = 'test@newemailaddress.xyz';
-        $order->setEmail($email);
+        $user = \Craft::$app->getUsers()->ensureUserByEmail($email);
+        $order->setCustomer($user);
         /** @var Order $order */
         $completedOrder = $this->tester->grabFixture('orders')->getElement('completed-new');
         $lineItem = $completedOrder->getLineItems()[0];
@@ -80,7 +81,7 @@ public function testUpdatedProperties(): void
         self::assertEquals($email, $order->orderCompletedEmail);
 
         $this->_deleteElementIds[] = $order->id;
-        $this->_deleteElementIds[] = $order->getCustomerId();
+        $this->_deleteElementIds[] = $user->id;
     }
 
     /**
diff --git a/tests/unit/services/CartsTest.php b/tests/unit/services/CartsTest.php
index ceedb49fb9..aac96a20af 100644
--- a/tests/unit/services/CartsTest.php
+++ b/tests/unit/services/CartsTest.php
@@ -13,6 +13,7 @@
 use craft\commerce\Plugin;
 use craft\commerce\services\Carts;
 use craftcommercetests\fixtures\CustomerAddressFixture;
+use craftcommercetests\fixtures\CustomerFixture;
 use UnitTester;
 
 /**
@@ -31,6 +32,9 @@ class CartsTest extends Unit
     public function _fixtures(): array
     {
         return [
+            'customer' => [
+                'class' => CustomerFixture::class,
+            ],
             'customerAddresses' => [
                 'class' => CustomerAddressFixture::class,
             ],
@@ -60,17 +64,16 @@ public function testGetCartAutoSetAddresses(string $email, bool $autoSet, bool $
             },
         ]));
 
+        $user = Craft::$app->getUsers()->getUserByUsernameOrEmail($email);
         if ($loggedIn) {
-            $user = Craft::$app->getUsers()->getUserByUsernameOrEmail($email);
             Craft::$app->getUser()->setIdentity($user);
             Craft::$app->getUser()->getIdentity()->password = $user->password;
         }
 
         $newCart = new Order();
-        $newCart->setEmail($email);
+        $newCart->setCustomer($user);
         $newCart->number = $cartNumber;
         Craft::$app->getElements()->saveElement($newCart, false);
-        // Plugin::getInstance()->getCarts()->__set('cart', $newCart);
 
         $cart = Plugin::getInstance()->getCarts()->getCart();
 
@@ -97,4 +100,39 @@ public function getCartDataProvider(): array
             'logged-in-user-auto-set-addresses' => ['cred.user@crafttest.com', true, true, true, true],
         ];
     }
+
+    public function testGetCartSwitchCustomer(): void
+    {
+        $cartNumber = Plugin::getInstance()->getCarts()->generateCartNumber();
+        Plugin::getInstance()->set('carts', $this->make(Carts::class, [
+            'getSessionCartNumber' => function() use ($cartNumber) {
+                return $cartNumber;
+            },
+        ]));
+
+        $inactiveUser = $this->tester->grabFixture('customer')->getElement('inactive-user');
+        $credUser = $this->tester->grabFixture('customer')->getElement('credentialed-user');
+        $originalIdentity = Craft::$app->getUser()->getIdentity();
+        Craft::$app->getUser()->setIdentity($credUser);
+        Craft::$app->getUser()->getIdentity()->password = $credUser->password;
+
+
+        $order = new Order();
+        $order->number = $cartNumber;
+        $order->setCustomer($inactiveUser);
+
+        Craft::$app->getElements()->saveElement($order, false);
+        self::assertEquals($inactiveUser->id, $order->getCustomerId());
+
+        $cart = Plugin::getInstance()->getCarts()->getCart();
+
+        // assert customer has changed;
+        self::assertNotEquals($inactiveUser->id, $cart->getCustomerId());
+        self::assertEquals($credUser->id, $cart->getCustomerId());
+        self::assertEquals($credUser->email, $cart->getEmail());
+
+        // Reset data
+        Craft::$app->getUser()->setIdentity($originalIdentity);
+        Craft::$app->getElements()->deleteElement($cart, true);
+    }
 }
diff --git a/tests/unit/services/OrdersTest.php b/tests/unit/services/OrdersTest.php
index d7ce3c5fb1..5b3e9a08f8 100644
--- a/tests/unit/services/OrdersTest.php
+++ b/tests/unit/services/OrdersTest.php
@@ -98,12 +98,15 @@ public function testGetOrdersByCustomer(): void
 
     public function testGetOrdersByEmail(): void
     {
-        $orders = $this->service->getOrdersByEmail($this->fixtureData->getElement('completed-new')->email);
+        /** @var Order $orderFixture */
+        $orderFixture = $this->fixtureData->getElement('completed-new');
+        $email = $orderFixture->getEmail();
+        $orders = $this->service->getOrdersByEmail($email);
 
         self::assertIsArray($orders);
         self::assertCount(3, $orders);
         foreach ($orders as $order) {
-            self::assertEquals($this->fixtureData->getElement('completed-new')->email, $order->email);
+            self::assertEquals($email, $order->getEmail());
         }
     }
 }