if you dont need the smtp route just delete the smtproutes file and restart qmail..
but take care if you send email directly from your box: a lot of providers are checking if a sending MX host has a PTR Record in DNS...and refuse connections if the sending mx has no PTR record....
also it might be possible that your plesk provider is firewalling smtp port 25...and only their smarthost is allowed to send emails throug firewall...
greets