This is a standard Plesk host with a slightly custom interface.
This host does not have email catch-all functionality. This means that incoming emailed subscriptions will only work if an email forwarder is defined in Plesk for each autoesponder to the arpReach email address you create during the installation process (normally email@example.com).
Use the following format for the cron definition.
/usr/bin/php /var/www/vhosts/yourdomain.com/httpdocs/a/a.php cli/auto
/usr/bin/php /var/www/vhosts/mysite.com/httpdocs/a/a.php cli/auto