Fortimail and received URLs. Is Web Rating override possible?

Hi, 

Is it possible on a fortimail (6.4.x) to implement Web Rating override on URLs contained on incoming emails?

Issue:

A colleague will send an email containing a URL to an internal resource, with an internal only domain name.

A response to the mail from the outside will be received by the fortimail which sees the internal domain as "Newly Observed Domain", and quarantined.

On a FortiOS based device, we could override this web rating. I don't see this option on the fortimail.

As it's an internal domain, it's unlikely to be accepted using https://www.fortiguard.com/webfilter

Workaround:

Fortimail's URL exemptions are a stopgap, but prone to failing with port / hostname changes. 

Not keen on using regex's due to lack of info (Just documented as perl-regex-alike), and possibility of creating a security hole.