Internally forwarded email blocked by ASE

Hello Forum users, 

I'm new to firewalling and have an issue with a company Fortigate 200B using firmware v5.2.9 build736 blocking an internal email as spam after whitelisting the email address. After allowing the email address in the whitelist the email now arrives to the recipient email within the company(as this was also blocked by ASE). The issue now is that the recipient can't forward the email internally as it is reported as "spam by ASE". I'd really appreciate some assistance on how I solve this issue as I've read in some forums to turn of ASE but not sure that this is a wise choice.