Automatic forwarding email on Linux/Unix
1. login your account from ssh connection with mail server
$ touch ~/.forward
$ echo 'account@forwarding.mail' >> ~/.forward
$ chmod 644 ~/.forward
2. Other account at the same server
$ su - # change to root
$ echo 'fromaccount: otheraccount' >> /etc/alias
$ newaliases
References
https://unix.stackexchange.com/questions/301310/how-can-i-automatically-forward-system-mail
https://kb.iu.edu/d/aeur