Email forwarding has gone through many changes so what you thought was true may not be true now.
myaccount.uchicago.edu is the portal to use to change your email forwarding.
When a CS account is created we forward all of your CS mail(cnetid@cs.uchicago.edu) to cnetid@uchicago.edu.
The only way to change your forwarding address is to ask us (techstaff@cs.uchicago.edu).