Hi, Stefano!
Please, I’m sorry. I found the reason why I did not have the job of the cron task.
I’m using a configurator to connect plug-ins (Plugin Load Filter), and your Newsletter plugin was only connected to the ‘subscription’ page and main page of site.
And i see in plugin.php code
functions admin_menu(){
...
$this->add_admin_page('diagnostic', 'Diagnostic');
...
}
But not see in real menu? Why?