When you first sign up the email address provided at sign up is where all invoices and receipts are sent by default.
However if you have a dedicated accounts department, or a bookkeeper who you would prefer receive your receipts you can update this in the system from your web portal logins.
Step 1. Log in to the Web Portal
Step 2. Click on Settings from the left navigation menu
Step 3. The section that shows Postal Address etc.. click on Edit Details
Step 4. in the field called "Billing Email" enter the email address you want future receipts emailed to