Allow to overwrite the email template again

Signed-off-by: Joas Schilling <coding@schilljs.com>

config/config.sample.php

@@ -966,6 +966,13 @@ $CONFIG = array(
  */
 'systemtags.managerFactory' => '\OC\SystemTag\ManagerFactory',
 
+/**
+ * Replaces the default mail template layout. This can be utilized if the
+ * options to modify the mail texts with the theming app is not enough.
+ * The class must extend  ``\OC\Mail\EMailTemplate``
+ */
+'mail_template_class' => '\OC\Mail\EMailTemplate',
+
 /**
  * Maintenance
  *

lib/private/Mail/Mailer.php

@@ -90,6 +90,16 @@ class Mailer implements IMailer {
 	}
 
 	public function createEMailTemplate() {
+		$class = $this->config->getSystemValue('mail_template_class', '');
+
+		if ($class !== '' && class_exists($class) && is_a($class, EMailTemplate::class, true)) {
+			return new $class(
+				$this->defaults,
+				$this->urlGenerator,
+				$this->l10n
+			);
+		}
+
 		return new EMailTemplate(
 			$this->defaults,
 			$this->urlGenerator,