Nelson writes about trying to sign up at Amazon:

When trying to create an account, I was told an account already existed with the email I was trying to use (and they were right, I have a AWS account with that email). So I tried to sign in using that email. Then I was told they couldn’t find an account with that same email address. Odd. I tried signing into AWS with that email and sure enough I got in. It looks like emails associated with AWS cannot be used to create an account for AWS certifications, which is a bit ironic.

Thanks Nelson for the submission!