In case you’re wondering how to customize your email notices that Magento sends out, it may take you a while to find the files that need editing. The stock Magento emails have goofy things in the emails like Demo Store and dummyemail@magento.com. There is also the stock Magento Demo Store logo on the emails. Not really what you want going out to customers!
First of all, upload your logo that you want on the emails to the following directory: /skin/frontend/default/yourtheme/images/
The image needs to be named logo_email.gif unless you want to change it in all the files mentioned in the next section of the article.
Next you need to open all of the files in the /app/locale/en_US/template/email/ directory, including the /sales/ directory as well. Find all occurrences of the “Demo Store“, dummyemail@magento.com, magento@varien.com, the (555) 555-0123 phone number and the alt tag for the logo from “Magento” and change all those values to your own.