Nice plugin but I get a PHP fatal error on trying to send the test email :
PHP Fatal error: Call to undefined function home_url() in /var/www/vhosts/x.org/httpdocs/wp-content/plugins/update-notifier/update-notifier.php on line 196, referer: http://www.x.org/wp-admin/options-general.php?page=update-notifier
It seems this will not happen in the test email only. Is there another file to include ? Not sure why that function is not found.