aliases : Change root: postfix to root: VALID EMAIL_ in /etc/aliases!!!
canonical: Add entry for local root: root root@HOSTNAME.ethz.ch
main.cf:
Set myhostname = HOSTNAME.ethz.ch
Set mydomain = hbt.arch.ethz.ch
Set myorigin = $mydomain
Add canonical_maps = hash:/etc/postfix/canonical
Call newaliases
Call postmap canonical
Monitor /var/log/maillog
Send test mails from root to local user, from local user to root
The entry in canonical is needed so mail does not get sent to root@hbt.arch.ethz.ch. The entry in aliases is recommended by postfix setup. Settings myhostname is most likely unnecessary but there for completeness. mydomain is used for rewriting of outgoing mails. With standard settings of postifx only mail from 127.0.0.1 will be accepted, none from available non-local interfaces. Drawback of this configuration is, that no local mail is stored and if a mail is locally sent to an account without canonical entry it will end up at user@hbt.arch.ethz.ch.