If you have a list of pre-generated keys, you can enable the Send Stored Codes option in your product's settings, which will provide a place to paste in your list of codes -- see further details here:
http://www.e-junkie.com/ej/help.selling-codes.htm
If you are selling a file download that you wish to have us deliver to your buyers, you would simply upload that file to our server when adding the download product in your E-junkie Seller Admin. You can enable both Single File Download and Send Stored Codes on the same product.
After the buyer finishes checkout, and once the payment processor notifies us they have completed the buyer's payment, we grant the buyer access to a thank-you page we automatically generate for their transaction, where we would present their unique download link(s). Every download link we issue expires after the number of Attempts or Hours (whichever comes first) that you specify in each product's settings.
We also send the buyer a thank-you email message with their unlock code (from the list of codes you pasted) and a link to reach their thank-you/download page in case they did not proceed there after checkout.
