@ChrisR
Does VIN allow you to utilize an outside IP or MX records? If so, it may be a good idea to look at getting your own dedicated IP/Email server from Mandrillapp or Sendgrid utilizing your domain. Again, I am not sure if VIN allows you to use a third party email platform. If they do, this would most likely solve your problem. Maybe VIN (and other CRM companies) can offer dedicated IP address to dealers as a way to protect email reputations.
One more thing you might want to do is create your own Sparklight email account and utilize that to contact their support team about your email situation (you should send your Sparklight email address an email from your CRM and reference that to them).