diff --git a/src/Queue/Task/EmailTask.php b/src/Queue/Task/EmailTask.php
index 900b0c95..2e4f10d6 100644
--- a/src/Queue/Task/EmailTask.php
+++ b/src/Queue/Task/EmailTask.php
@@ -164,7 +164,7 @@ public function run(array $data, int $jobId): void {
 
 		$settings = $data['settings'] + $this->defaults;
 
-		foreach (['to', 'from', 'cc', 'bcc', 'replyTo', 'sender', 'returnPath'] as $addressMethod) {
+		foreach (['to', 'from', 'cc', 'bcc', 'replyTo', 'sender', 'returnPath', 'readReceipt'] as $addressMethod) {
 			if (!array_key_exists($addressMethod, $settings)) {
 				continue;
 			}
@@ -174,6 +174,35 @@ public function run(array $data, int $jobId): void {
 			unset($settings[$addressMethod]);
 		}
 
+		// Message body keys from a serialized Message payload use different names than
+		// their setter methods. Route them explicitly so the generic loop does not try
+		// to call nonexistent `setHtmlMessage`/`setTextMessage` on the Mailer.
+		if (array_key_exists('htmlMessage', $settings)) {
+			$this->mailer->getMessage()->setBodyHtml((string)$settings['htmlMessage']);
+			unset($settings['htmlMessage']);
+		}
+		if (array_key_exists('textMessage', $settings)) {
+			$this->mailer->getMessage()->setBodyText((string)$settings['textMessage']);
+			unset($settings['textMessage']);
+		}
+
+		// `headers` must be passed as a single positional argument — the map's string
+		// keys would otherwise be interpreted as named parameters under PHP 8.
+		if (array_key_exists('headers', $settings)) {
+			$this->mailer->getMessage()->setHeaders((array)$settings['headers']);
+			unset($settings['headers']);
+		}
+
+		// `appCharset` has no setter on Mailer or Message. Fall back to the Message
+		// charset when a dedicated `charset` value was not also provided.
+		if (array_key_exists('appCharset', $settings)) {
+			$appCharset = (string)$settings['appCharset'];
+			unset($settings['appCharset']);
+			if (!array_key_exists('charset', $settings)) {
+				$this->mailer->getMessage()->setCharset($appCharset);
+			}
+		}
+
 		foreach ($settings as $method => $setting) {
 			$setter = 'set' . ucfirst($method);
 			if (in_array($method, ['theme', 'template', 'layout'], true)) {
diff --git a/tests/TestCase/Queue/Task/EmailTaskTest.php b/tests/TestCase/Queue/Task/EmailTaskTest.php
index 4eb79b16..e6523879 100644
--- a/tests/TestCase/Queue/Task/EmailTaskTest.php
+++ b/tests/TestCase/Queue/Task/EmailTaskTest.php
@@ -253,6 +253,72 @@ public function testRunArrayAssociativeAddressMap() {
 		$this->assertSame(['reply@test.de' => 'Reply Name'], $mailer->getReplyTo());
 	}
 
+	/**
+	 * Settings keys coming from a JSON-round-tripped `Message::__serialize()` payload
+	 * (e.g. `htmlMessage`, `textMessage`, `appCharset`) must not be routed to
+	 * nonexistent `set<Prop>()` methods on the Mailer.
+	 *
+	 * @return void
+	 */
+	public function testRunArrayMessageSerializableProperties() {
+		$settings = [
+			'from' => 'sender@test.de',
+			'to' => 'recipient@test.de',
+			'subject' => 'Message Subject',
+			'domain' => 'example.com',
+			'charset' => 'utf-8',
+			'headerCharset' => 'utf-8',
+			'appCharset' => 'UTF-8',
+			'emailFormat' => 'html',
+			'messageId' => true,
+			'htmlMessage' => '<p>Hello</p>',
+			'textMessage' => 'Hello',
+		];
+
+		$data = [
+			'settings' => $settings,
+		];
+		$this->Task->run($data, 0);
+
+		$this->assertInstanceOf(Mailer::class, $this->Task->mailer);
+
+		$message = $this->Task->mailer->getMessage();
+		$this->assertSame('Message Subject', $message->getSubject());
+		$this->assertSame('example.com', $message->getDomain());
+		$this->assertSame('html', $message->getEmailFormat());
+		$this->assertSame('utf-8', $message->getCharset());
+		$this->assertSame('utf-8', $message->getHeaderCharset());
+	}
+
+	/**
+	 * An associative `headers` map inside `settings` must not be expanded into named
+	 * parameters when calling `Message::setHeaders()`.
+	 *
+	 * @return void
+	 */
+	public function testRunArrayHeadersInSettings() {
+		$settings = [
+			'from' => 'sender@test.de',
+			'to' => 'recipient@test.de',
+			'headers' => [
+				'X-Custom' => 'queued',
+				'X-Other' => 'value',
+			],
+		];
+
+		$data = [
+			'settings' => $settings,
+			'content' => 'Foo Bar',
+		];
+		$this->Task->run($data, 0);
+
+		$this->assertInstanceOf(Mailer::class, $this->Task->mailer);
+
+		$headers = $this->Task->mailer->getMessage()->getHeaders(['_headers']);
+		$this->assertSame('queued', $headers['X-Custom']);
+		$this->assertSame('value', $headers['X-Other']);
+	}
+
 	/**
 	 * @return void
 	 */