Postfix relay works but with wrong return-path.

I’ve read a few posts but I still can’t send e-mails the right way.
This is my setup:
vpserver - hosts my server and my e-mails (DNS MX records are ok)
myhost - has a fresh clean install of ubuntu 12.04 and virtualadmin installed flawless.

Now, I’ve setup at my vpserver.
Also, I’ve installed Mail Relay plugin at virtualadmin and configured it.
I can send e-mails through my application, but the return-path is always:

Need some help. This is driving me insane, I’ve checked Transport Mapping, Rewriting and Masquerading, etc…