Googlemail users can't email my email address
It looks like your domain is rejecting e-mails:
Google tried to deliver your message, but it was rejected by the recipient domain.
Have you tried any other sources for e-mail to see if it's a general problem or if it's just rejecting e-mails from gmail.com.
Double check that you've set up the mail part of your GridServer account correctly.
After than, I'd check with MediaTemple to see if they can shed some light on the problem.