Setup email defaults but not using default contact

Select Sales

Customer Maintenance

Search for the Customer Account via the QuickBar

Click Edit Addresses

Click Contacts at the bottom left corner

Press Enter

List of all contacts related to the company should appear

Make sure the contact in question has a Email address

Now on the Sub menu click Email Defaults

Tick all relevant documents

Now when a invoice for example is printed, the option to email them instead will appear