OkiOki has a personal email address ready for you. Any mail or documents you forward to this address will be automatically picked up by OkiOki. If the invoice is added as an attachment, it will pick up the attachment. If the mail itself is an invoice, it will process the entire email as an invoice.
Your OkiOki email address can be found in the menu under 'Your account'.
You can easily copy this address in OkiOki and paste it into Outlook, for example, and save it as the destination address.