Email Internally Bounce And Give A 550 Error

I found that the domain name was hosted at enom.com and the email was gmail. The web servers are both Media Temple servers.we updated the settings on the new server using google's instructions. However, it is still not working properly. So, to be as clear as possible, here is the specifics:

Email from the outside works fine, Email internal to external works fine, email internally (from one emplyee to another internally) will bounce giving a 550 error. After researching this error, I found that several people have had this issue, however, the majority of the fixes didn't work.