The /etc/mail_aliasesconfiguration > server > email > aliases
/etc/aliases contains who is available under which address.
The file format is
An entry for the
root user can redirect all EMails for this user to an
external mail address. Alternatively every user can create a
$HOME to forward local mails to another address.
For that to work a mail-transport-agent like postfix must be reachable via that machine.