Added support for german Umlaute.

module.php

@@ -262,6 +262,11 @@ return new class extends Lewp\Module
             'From: '.$options[self::OPTIONS_MAIL_FROM]
             ."\r\n"
             .'Reply-To: '.$payload[self::KEY_POST_EMAIL]
+            ."\r\n"
+            .'MIME-Version: 1.0'
+            ."\r\n"
+            .'Content-type: text/plain; charset=UTF-8'
+            ."\r\n"
         );
     }