When using Payments Standard you will not have the option to generate the email receipt in the checkout wizard. This is because Payments Standard is a remote checkout and the status of the transaction is not known at the time of the transaction. You can only get the details of the transaction after the fact.
If you are using Payments Standard it is much more difficult to get back the details of a transaction. You will need to make use of IPN to get the information about the order. Here is a link to PayPal's site about IPN:
You could setup your IPN page to listen for a response from PayPal, then when the order's info is posted to your IPN page you can check to ensure it was successful then send an email with Universal Email.