Mail sends to other users though, just not that address. I was thinking it was return from his ISP.
Also, I followed that link and yes, both of my name servers are from the same location. That's not something I'm too worried about. I don't know how I would be able to use a name server at a different location because I only have 1 IP address.
In the DNS Manager, I select plastikracing.net
as the domain and this is what shows for the MX records: