When I send a mail with PHP the destinatary gets a header like this one:
noreply@justwalk.it **via** de p3nlhg147.shr.prod.phx3.secureserver.net >
noreply@justwalk.it **via** de p3nlhg147.shr.prod.phx3.secureserver.net
See what Google says about this here: http://support.google.com/mail/bin/answer.py?hl=en&ctx=mail&answer=1311182
All the best!