diff --git a/src/Monolog/Handler/MailHandler.php b/src/Monolog/Handler/MailHandler.php
index 640af29e..2b9d74c8 100644
--- a/src/Monolog/Handler/MailHandler.php
+++ b/src/Monolog/Handler/MailHandler.php
@@ -11,6 +11,9 @@
 
 namespace Monolog\Handler;
 
+use Monolog\Formatter\FormatterInterface;
+use Monolog\Formatter\HtmlFormatter;
+
 /**
  * Base class for all mail handlers
  *
@@ -64,4 +67,19 @@ abstract class MailHandler extends AbstractProcessingHandler
 
         return $highestRecord;
     }
+
+    protected function isHtmlBody($body)
+    {
+        return substr($body, 0, 1) === '<';
+    }
+
+    /**
+     * Gets the default formatter.
+     *
+     * @return FormatterInterface
+     */
+    protected function getDefaultFormatter(): FormatterInterface
+    {
+        return new HtmlFormatter();
+    }
 }
diff --git a/src/Monolog/Handler/MandrillHandler.php b/src/Monolog/Handler/MandrillHandler.php
index e30f603a..1fb9dc6a 100644
--- a/src/Monolog/Handler/MandrillHandler.php
+++ b/src/Monolog/Handler/MandrillHandler.php
@@ -48,8 +48,13 @@ class MandrillHandler extends MailHandler
      */
     protected function send($content, array $records)
     {
+        $mime = null;
+        if ($this->isHtmlBody($content)) {
+            $mime = 'text/html';
+        }
+
         $message = clone $this->message;
-        $message->setBody($content);
+        $message->setBody($content, $mime);
         $message->setDate(time());
 
         $ch = curl_init();
diff --git a/src/Monolog/Handler/NativeMailerHandler.php b/src/Monolog/Handler/NativeMailerHandler.php
index f6fb0430..4289e35e 100644
--- a/src/Monolog/Handler/NativeMailerHandler.php
+++ b/src/Monolog/Handler/NativeMailerHandler.php
@@ -56,7 +56,7 @@ class NativeMailerHandler extends MailHandler
      * The Content-type for the message
      * @var string
      */
-    protected $contentType = 'text/plain';
+    protected $contentType;
 
     /**
      * The encoding for the message
@@ -117,10 +117,15 @@ class NativeMailerHandler extends MailHandler
      */
     protected function send($content, array $records)
     {
-        $content = wordwrap($content, $this->maxColumnWidth);
+        $contentType = $this->getContentType() ?: ($this->isHtmlBody($content) ? 'text/html' : 'text/plain');
+
+        if ($contentType !== 'text/html') {
+            $content = wordwrap($content, $this->maxColumnWidth);
+        }
+
         $headers = ltrim(implode("\r\n", $this->headers) . "\r\n", "\r\n");
-        $headers .= 'Content-type: ' . $this->getContentType() . '; charset=' . $this->getEncoding() . "\r\n";
-        if ($this->getContentType() == 'text/html' && false === strpos($headers, 'MIME-Version:')) {
+        $headers .= 'Content-type: ' . $contentType . '; charset=' . $this->getEncoding() . "\r\n";
+        if ($contentType === 'text/html' && false === strpos($headers, 'MIME-Version:')) {
             $headers .= 'MIME-Version: 1.0' . "\r\n";
         }
 
diff --git a/src/Monolog/Handler/SendGridHandler.php b/src/Monolog/Handler/SendGridHandler.php
index 14395509..cee69861 100644
--- a/src/Monolog/Handler/SendGridHandler.php
+++ b/src/Monolog/Handler/SendGridHandler.php
@@ -82,9 +82,14 @@ class SendGridHandler extends MailHandler
             $message['to[]'] = $recipient;
         }
         $message['subject'] = $this->subject;
-        $message['text'] = $content;
         $message['date'] = date('r');
 
+        if ($this->isHtmlBody($content)) {
+            $message['html'] = $content;
+        } else {
+            $message['text'] = $content;
+        }
+
         $ch = curl_init();
         curl_setopt($ch, CURLOPT_URL, 'https://api.sendgrid.com/api/mail.send.json');
         curl_setopt($ch, CURLOPT_POST, 1);
diff --git a/src/Monolog/Handler/SwiftMailerHandler.php b/src/Monolog/Handler/SwiftMailerHandler.php
index 92e3e939..44026fc3 100644
--- a/src/Monolog/Handler/SwiftMailerHandler.php
+++ b/src/Monolog/Handler/SwiftMailerHandler.php
@@ -72,7 +72,12 @@ class SwiftMailerHandler extends MailHandler
             $message->setSubject($subjectFormatter->format($this->getHighestRecord($records)));
         }
 
-        $message->setBody($content);
+        $mime = null;
+        if ($this->isHtmlBody($content)) {
+            $mime = 'text/html';
+        }
+
+        $message->setBody($content, $mime);
         $message->setDate(time());
 
         return $message;
diff --git a/tests/Monolog/Handler/MailHandlerTest.php b/tests/Monolog/Handler/MailHandlerTest.php
index e6169325..c489e263 100644
--- a/tests/Monolog/Handler/MailHandlerTest.php
+++ b/tests/Monolog/Handler/MailHandlerTest.php
@@ -61,6 +61,7 @@ class MailHandlerTest extends TestCase
     public function testHandle()
     {
         $handler = $this->getMockForAbstractClass('Monolog\\Handler\\MailHandler');
+        $handler->setFormatter(new \Monolog\Formatter\LineFormatter);
 
         $record = $this->getRecord();
         $records = [$record];
diff --git a/tests/Monolog/Handler/NativeMailerHandlerTest.php b/tests/Monolog/Handler/NativeMailerHandlerTest.php
index 6d0fc487..9ac08be6 100644
--- a/tests/Monolog/Handler/NativeMailerHandlerTest.php
+++ b/tests/Monolog/Handler/NativeMailerHandlerTest.php
@@ -78,6 +78,7 @@ class NativeMailerHandlerTest extends TestCase
         $from = 'receiver@example.org';
 
         $mailer = new NativeMailerHandler($to, $subject, $from);
+        $mailer->setFormatter(new \Monolog\Formatter\LineFormatter);
         $mailer->handleBatch([]);
 
         // batch is empty, nothing sent