There is a nice feature in OpenMail.SG that is worthed mentioning - Email Forwarding Tracking for Administrator.
Some of our corporate customers asked for this feature. We thought over it and asked ourselves "Why Not?".
This is a feature that allows administrators to track the forwarded email addresses.
Note that only privileged users (usually the HR or Security teams or the Business Owners) will be allowed this feature.
There are some corporate rules that disallow employees to forward their emails to external parties. Thus this feature allows the administrators to quickly identify employees who might have accidentally forwarded to non-intended parties.