Problems with finding your Kindle or whitelisted emails? Check out this guide:
1. Navigate to https://www.amazon.com/mn/dcw/myx.html (it's official Amazon page, so don't worry to log in if you're not). Remeber to login to account binded with your Kindle device.
2. Navigate to 'Settings' tab.
3. Scroll down to ' Personal Document Settings' section.
4. You'll see 2 tables with e-mail adresses you're asked for in the app.