In general that'd be fine. The sender address can be easily spoofed anyway - smtp works that way.
The thing is, this seems to be broken by design in my world. Google should (have to check that again) publish a record that lists 'official' mail servers for GMail.
This whole setup could work just fine, even if it's a bit weird. But right now I suppose you look like a crappy imposter to any receiver AND you can never receive emails (they .. would end up in your GMail inbox of course).
