Your SPF DNS record doesn't allow Gmail to send on behalf of your domain (openrigs.com). Fixing that should resolve the issue.
ie, "v=spf1 mx ptr a:geartri.be a:mailer.openrigs.com include:_spf.google.com ~all"
Thanks - I've made the change, but I'm confused...the mails are going from mailer.openrigs.com to a server as dictated by gmail.com's MX record...why does it need to have anything other than a:mailer.openrigs.com to allow it? My SPF-fu is bad:)