If you are using Google Apps for email delivery, but your domain is still running on an external server that needs to deliver to those accounts, you can run into a lot of trouble with mail delivery. In the case of a server running Plesk, the MTA is qmail, but sendmail has the same type of problem. Basically it, by default, ignores the DNS settings and tries to deliver mail locally when it can – which is clearly not what you want.
These steps are needed:
- Turn off any DNS server that might be running locally.
- Comment out the instances of the domain from the 3 configuration files listed here.
- Restart the qmail service.
Hope this helps.