Server :: Plesk 9 - Send Domain Mail To Offsite / External Host

I am managing a Fedora dedicated server with Plesk 9 and just recently moved the email for one of the domains on the server to Google Apps for business. Unfortunately, I cannot get email messages from the website forms to deliver to addresses on this domain. For anyone familiar with Plesk, I have disabled mail in the hosting settings by un-checking the "Activate mail service on domain" checkbox and there are no accounts in the domain. (Other readings have indicated that this should be enough to allow mail to be directed to the appropriate server). My MX records correctly point to the google apps mail server.

I'm quite comfortable with command line, but I know almost nothing about the sendmail program or its alternatives and my attempts at researching how to set up this relay has been futile. I'm pretty sure I'm using sendmail and not qmail or anything else from what the red-hat style "alternatives" symlinks point to. I've also checked the /etc/mail/access, domaintable, mailertable, sendmail.cf, virtusertable, local-host-names, sendmail.cf, and submit.cf and most of these files are empty (except the .cf files), and the sendmail.cf and submit.cf make no reference to the domain in question.

Here is the output from a sendmail test that was was not received. (Private data omitted of course).
sendmail -v xxx@yyy.com
test email from yyy.com webserver. please ignore.
xxx@yyy.com... Connecting to [127.0.0.1] via relay...
220 my.server.com ESMTP
>>> EHLO my.server.com
250-my.server.com .....
Closing connection to [127.0.0.1]
>>> QUIT

Performing the same test and sending an email to a non-hosted domain works fine.