Step 10. I was working on the basis that you could work off the "copy to sender" email even if the destination email was invalid, but I haven't tried it so I don't know. It only takes about 60 seconds to set up a throwaway email on yahoo anyway, so maybe that's the safest way to go.
AFAIK the code works regardless of email address anyway, i.e. the next account doesn't have to use the email the code was sent to.