Thanks for the hook fep_save_announcement. I’ve written the following:

add_action( 'fep_save_announcement', 'send_something', 100, 3 );

function send_something( $message_id, $message, $inserted_message )
{
    echo '<pre>';
    print_r($message_id);
    echo '</pre>';

    echo '<pre>';
    print_r($message);
    echo '</pre>';

    echo '<pre>';
    print_r($inserted_message);
    echo '</pre>'; die;
}

But in my $message variable I don’t see how I can get the receivers of the announcement. Do you know how I can get it?