An email was sent from Kim to Alex. After the email being sent, received, and read, both Kim and Alex deleted and overwrote the storage spaces for the email data in their respective computers. Which of the following statements is correct?

a$.$ The email data can be restored via data carving.

b$.$ The email data can be recovered by using undelete tools of the file systems.

c$.$ A copy of the email data may exist somewhere on the Internet.

d$.$ The email data are gone forever and are irrecoverable.