There is a bug within Magento 1 Core API where the customer email does not get added to the order upon guest checkout. Hence, MyDeal is unable to fix this for you - you would need to fix it yourself.
- customer_email is set correctly to
shoppingCartCustomerAddressescall, the email gets copied to billing address, but from
quote->getCustomer()->getEmail(), which is empty for guest customers
shoppingCartOrdercall, customer_email is then copied from the empty value in the billing address
- As a result, the order is created with a blank customer email
How to fix this bug? Please refer to this ARTICLE to assist you in resolving the bug