Permission denied when doing Postfix ubuntu tutorial

Question

Im working on this tutorial Postfix mail server. https://help.ubuntu.com/community/Postfix

When i run the command. su - fmaster mail

I get the error. Cannot open mailbox /var/mail/fmaster: Permission denied No mail for fmaster

also i sign in as fmaster. terminal -> mail.

/var/mail/fmaster: Permission denied No mail for fmaster

Answer 1

           sudo touch /var/mail/$USER
           sudo chown $USER:mail /var/mail/$USER
           sudo chmod o-r /var/mail/$USER
           sudo chmod g+rw /var/mail/$USER