Here is a step by step guide on how to find the approved emails on your Amazon account and how to add one if the one you have isn't listed.
Please log into your Amazon account from a computer. This guide is written from the computer perspective.
Go to My Account
Scroll down to the Digital Content Section.
Find Manage your Kindle
On the left side panel under the Your Kindle Account, select Personal Document Settings.
On the next screen, the section labeled Approved Personal Document E-mail List is where you want to see if the email you have is listed.
If the email is not listed, you will need to add it.In the box that pops up, put in the email you want to use to send files to your Kindle device.
Then click the add email button.
The email should now be listed and ready to use.
Once you see it there, you can begin sending files to your Kindle from that email address.