If you believe the theft coverage included in your property policy would cover you if you transferred money or products due to an email or even phone call scam, you are likely mistaken. Most property policies exclude such coverage in a number of places.
For instance, property that has been transferred to a person or to a place outside the described premises on the basis of unauthorized instructions and voluntary parting with any property by you or anyone else to whom you have entrusted the property if induced to do so by any fraudulent scheme, trick, device or false pretense are normally excluded in property policies. In the first series I discussed policies that can assist with risk prevention.
Your second defense is simple training for all employees and more advanced training for those employees who are authorized to transfer your funds. The training at the very least should train all employees to refer any requests for money to one or a small handful of employees. For those authorized to transfer funds, they should be trained on how to identify these potentially fraudulent requests.