Malcolm Young
--- a/src/Controller/MaillogController.php
+++ b/src/Controller/MaillogController.php
+    $mail['html_headers'] = $html['headers'];
+    $mail['html_body'] = $html['body'];
+
+    $output = [
+      '#type' => 'container',
+    ];
+
+    foreach ($mail as $section => $contents) {
+      if (substr($section, 0, 5) == 'other') {
+        continue;
+      }
+
+      switch ($section) {
+        case 'html_body':
+          $encoded = implode('', $contents);
+          $decoded = base64_decode($encoded);
--- a/src/Controller/MaillogController.php
+++ b/src/Controller/MaillogController.php
+   *   True if it is a boundary line.
+   */
+  protected function isBoundary($line) {
+    if (str_starts_with($line, '--')) {
+      if (strlen($line) == 43) {
+        return TRUE;
+      }
+
+      if (strlen($line) == 45 && str_ends_with($line, '--')) {
+        return TRUE;
+      }
+    }
+
+    return FALSE;
+  }
+
--- a/src/Controller/MaillogController.php
+++ b/src/Controller/MaillogController.php
+      ];
+    }
+
+    return $output;
+  }
+
+  /**
+   * Check whether a line is a multipart boundary.
+   *
+   * @param string $line
+   *   The line from the email.
+   *
+   * @return bool
+   *   True if it is a boundary line.
+   */
+  protected function isBoundary($line) {
--- a/src/Controller/MaillogController.php
+++ b/src/Controller/MaillogController.php

 use Drupal\Component\Utility\Html;
 use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Render\Markup;