I have a Exchange 2013 OWA URL that hits the Fortigate, which in turn performs a NAT to my KEMP load balancers.  One of the things I want to do is redirect HTTP to HTTPS with the KEMP.  Unfortunately the Fortigate hijacks any 80 requests and throws up the 403 Forbidden warning.

 

 

In order to stop this from happening and let the HTTP traffic straight through I had to disable IPS from the policy and presto problem solved.