To add an Email address for billing purposes:
By default your login email will always be included on any billing notifications including invoices, receipts, and any other statements pertinent to the accounting/billing for the SRFax account. There is an option to also include additional email addresses for this notifications. To add additional billing contacts for your account first log into your account and then navigate to "My Account" then "Billing Details" and add the Email in the section name "Billing Notifications" at the bottom of the page.
Any changes made will be saved after you click on UPDATE.