We have a couple employees who love Gmail and refuse to use Outlook. That’s cool, whatever tool works. The big problem is when you send mail from Gmail — it is impossible to hide the “gmail.com” label Google automatically adds the “on behalf of” copy in the send header.

Check this out:

The consensus is that it can’t be fixed, it’s just something Google did to spread branding. Oddly, Yahoo mail doesn’t do this.