Technically, there’s no way to get the email address of the person who built the app. First, you can have multiple email addresses that map to the same username (for example, I am ewpatton@gmail.com and ewpatton@appinventor.mit.edu, both will yield the same ai_ewpatton). Second, people can repackage their apps (e.g., AppToMarket) using a package name that is different from the one used to compile.
If we can take a step back to the 30k foot view, what would be the purpose of knowing this information?