how does the unregistered emails works?

[Subtate]

Well... i don't know

[Reese]

They are emails that are connected to a Neopets account and expired with the provider . You register the email and then retrieve the Neopets information ^_^

[Carrot]

You find emails that are linked to neopets accounts. After a certain amount of time of no one using the email, they are deleted from the database and can be recreated. The neopets account will still be linked to the email address, so you will be able to access the neopets account if you are able to find an unreg email.

[Spectre257]

Here is a few guides I found about them, maybe these can help you out.
(you need an account to see links)
(you need an account to see links)