auto ebay script solution that emails customers

I have an ebay account which has fallen below standard due to slow shipping of goods. So i plan to sell some codes (low value) to every person that pays. What I need is a script so that when every person pays, it emails them a unique code. I have a list of codes in .csv file format. Each code can be used once only. It is too much work to email every person the next unused code, so I want a script or eBay API solution that just emails them the code, automatically when they pay. eg they buy 1 code, as soon as they pay it emails them one code. Some people buy 2 or 3 codes at a time, if they buy (and pay for) 3 codes it should email them 3 codes. Obviously the most important part is to mark the codes as "given out" in the input file or log. There are lots of ways to do this. I have 2 ebay accounts, selling manager pro, auctiva, ebay API access. You could use imacros. I dont mind provisioning a VPS for it. I will sell the codes at cost price or a little more and then after 1 month the feedback and detailed seller ratings (DSR's) will get better. My selling limits will raise. I have been selling on ebay for 6 years so I know their systems very very well. If you know what you are doing with eBay API, it should not be difficult. certainly, I could export all the sales via selling manager pro and run a mail merge, but this would mean that I have to sit down and run it once per day. I dont want to do that. It should be reliable. To keep things simple, I will sell only one product via the account however ideally i will sell codes + another physical product. I want customers to be happy.