diff --git a/dev/tests/integration/testsuite/Magento/Customer/Controller/AccountTest.php b/dev/tests/integration/testsuite/Magento/Customer/Controller/AccountTest.php
index 898d3ff400b38..b80f00b16f0bd 100644
--- a/dev/tests/integration/testsuite/Magento/Customer/Controller/AccountTest.php
+++ b/dev/tests/integration/testsuite/Magento/Customer/Controller/AccountTest.php
@@ -771,7 +771,7 @@ public function testConfirmationEmailWithSpecialCharacters(): void
 
         $this->assertContains('To: ' . $email, $rawMessage);
 
-        $content = $message->getBody()->getPartContent(0);
+        $content = $message->getBody()->getParts()[0]->getRawContent();
         $confirmationUrl = $this->getConfirmationUrlFromMessageContent($content);
         $this->setRequestInfo($confirmationUrl, 'confirm');
         $this->clearCookieMessagesList();
diff --git a/dev/tests/integration/testsuite/Magento/Newsletter/Model/SubscriberTest.php b/dev/tests/integration/testsuite/Magento/Newsletter/Model/SubscriberTest.php
index bcd4233655489..e971ca88c4e57 100644
--- a/dev/tests/integration/testsuite/Magento/Newsletter/Model/SubscriberTest.php
+++ b/dev/tests/integration/testsuite/Magento/Newsletter/Model/SubscriberTest.php
@@ -7,6 +7,9 @@
 
 use Magento\TestFramework\Mail\Template\TransportBuilderMock;
 
+/**
+ * \Magento\Newsletter\Model\Subscriber tests
+ */
 class SubscriberTest extends \PHPUnit\Framework\TestCase
 {
     /**
@@ -35,7 +38,7 @@ public function testEmailConfirmation()
         $this->assertContains(
             '/newsletter/subscriber/confirm/id/' . $this->model->getSubscriberId()
             . '/code/ysayquyajua23iq29gxwu2eax2qb6gvy',
-            $transportBuilder->getSentMessage()->getRawMessage()
+            $transportBuilder->getSentMessage()->getBody()->getParts()[0]->getRawContent()
         );
         $this->assertEquals(Subscriber::STATUS_NOT_ACTIVE, $this->model->getSubscriberStatus());
     }
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Create/SaveTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Create/SaveTest.php
index f863edd049258..6dba48092c400 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Create/SaveTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Create/SaveTest.php
@@ -142,7 +142,7 @@ public function testSendEmailOnOrderSave(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $assert);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $assert);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/AddCommentTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/AddCommentTest.php
index 2f23da8b3db87..13bcc756c2364 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/AddCommentTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/AddCommentTest.php
@@ -54,7 +54,7 @@ public function testSendEmailOnAddCreditmemoComment(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/SaveTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/SaveTest.php
index f589a0f5a1c74..13d1fe89f149a 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/SaveTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Creditmemo/SaveTest.php
@@ -56,7 +56,7 @@ public function testSendEmailOnCreditmemoSave(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/EmailTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/EmailTest.php
index 4d19106ad8e51..2addc4d40ecda 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/EmailTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/EmailTest.php
@@ -82,7 +82,7 @@ public function testSendOrderEmail(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $assert);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $assert);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/AddCommentTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/AddCommentTest.php
index 81e1dd7afc496..1db008690a154 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/AddCommentTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/AddCommentTest.php
@@ -55,7 +55,7 @@ public function testSendEmailOnAddInvoiceComment(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/EmailTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/EmailTest.php
index 85223528ec82a..b2f4b8a6954d5 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/EmailTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/EmailTest.php
@@ -59,7 +59,7 @@ public function testSendInvoiceEmail(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/SaveTest.php b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/SaveTest.php
index 68074e38d9a39..40540f3126899 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/SaveTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Controller/Adminhtml/Order/Invoice/SaveTest.php
@@ -51,7 +51,7 @@ public function testSendEmailOnInvoiceSave(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Sales/Model/Order/CreateTest.php b/dev/tests/integration/testsuite/Magento/Sales/Model/Order/CreateTest.php
index 1035ce1592314..3fe3fca260e8b 100644
--- a/dev/tests/integration/testsuite/Magento/Sales/Model/Order/CreateTest.php
+++ b/dev/tests/integration/testsuite/Magento/Sales/Model/Order/CreateTest.php
@@ -95,6 +95,6 @@ public function testSendEmailOnOrderPlace(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $assert);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $assert);
     }
 }
diff --git a/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/AddCommentTest.php b/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/AddCommentTest.php
index 25a44bab62994..a2ac5883a13d9 100644
--- a/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/AddCommentTest.php
+++ b/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/AddCommentTest.php
@@ -54,7 +54,7 @@ public function testSendEmailOnShipmentCommentAdd(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/SaveTest.php b/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/SaveTest.php
index 27b5bb02d4b22..e95e99224a6d9 100644
--- a/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/SaveTest.php
+++ b/dev/tests/integration/testsuite/Magento/Shipping/Controller/Adminhtml/Order/Shipment/SaveTest.php
@@ -51,7 +51,7 @@ public function testSendEmailOnShipmentSave(): void
         );
 
         $this->assertEquals($message->getSubject(), $subject);
-        $this->assertThat($message->getRawMessage(), $messageConstraint);
+        $this->assertThat($message->getBody()->getParts()[0]->getRawContent(), $messageConstraint);
     }
 
     /**
diff --git a/lib/internal/Magento/Framework/Mail/Message.php b/lib/internal/Magento/Framework/Mail/Message.php
index a9996c0a4f12a..b15b75ca9ac63 100644
--- a/lib/internal/Magento/Framework/Mail/Message.php
+++ b/lib/internal/Magento/Framework/Mail/Message.php
@@ -167,6 +167,8 @@ private function createMimeFromString($body, $messageType)
     {
         $part = new Part($body);
         $part->setCharset($this->zendMessage->getEncoding());
+        $part->setEncoding(Mime::ENCODING_QUOTEDPRINTABLE);
+        $part->setDisposition(Mime::DISPOSITION_INLINE);
         $part->setType($messageType);
         $mimeMessage = new \Zend\Mime\Message();
         $mimeMessage->addPart($part);
diff --git a/lib/internal/Magento/Framework/Mail/Test/Unit/MessageTest.php b/lib/internal/Magento/Framework/Mail/Test/Unit/MessageTest.php
index bea2a9ea91d38..c29ca4d261cc4 100644
--- a/lib/internal/Magento/Framework/Mail/Test/Unit/MessageTest.php
+++ b/lib/internal/Magento/Framework/Mail/Test/Unit/MessageTest.php
@@ -26,9 +26,10 @@ public function testSetBodyHtml()
 
         $part = $this->message->getBody()->getParts()[0];
         $this->assertEquals('text/html', $part->getType());
-        $this->assertEquals('8bit', $part->getEncoding());
+        $this->assertEquals('quoted-printable', $part->getEncoding());
         $this->assertEquals('utf-8', $part->getCharset());
         $this->assertEquals('body', $part->getContent());
+        $this->assertEquals('inline', $part->getDisposition());
     }
 
     public function testSetBodyText()
@@ -37,8 +38,9 @@ public function testSetBodyText()
 
         $part = $this->message->getBody()->getParts()[0];
         $this->assertEquals('text/plain', $part->getType());
-        $this->assertEquals('8bit', $part->getEncoding());
+        $this->assertEquals('quoted-printable', $part->getEncoding());
         $this->assertEquals('utf-8', $part->getCharset());
         $this->assertEquals('body', $part->getContent());
+        $this->assertEquals('inline', $part->getDisposition());
     }
 }