This page is about configuring the mail subsystem on a Raspberry Pi installed with RaspiOS, to be used as NAS and mediacenter. See the main index at Home Mediacenter and NAS with the Raspberry Pi.

I want a working mail system on the NAS, mainly because I want to eventually receive error messages from the various subsystems, think e.g. at the smartd daemon watching for S.M.A.R.T. hard drive errors…

In the following examples pimedianas is the hostname of my Raspberry Pi Mediacenter NAS. I istalled the postfix package and configured it as satellite system using a SMTP relay host. The relevant settings in /etc/postfix/main.cf are:

myhostname = pimedianas
mydestination = $myhostname, localhost.localdomain, localhost
relayhost = mail.example.org:587
default_transport = smtp
relay_transport = smtp
myorigin = $myhostname
# Rewrite some sender addresses.
sender_canonical_maps = hash:/etc/postfix/sender_canonical_maps
# Relay host requires SASL authentication.
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_mechanism_filter = plain, login
smtp_sasl_security_options =
smtp_tls_security_level = may

The content of /etc/postfix/sender_canonical_maps will force the MAIL FROM on locally generated mails:

root                       pimedianas@example.org
root@pimedianas            pimedianas@example.org
root@localhost             pimedianas@example.org
root@localhost.localdomain pimedianas@example.org

Write the proper info about localhost in /etc/hosts:

127.0.1.1  localhost.localdomain   localhost

Finally I had to put my SMTP credentials required by the relaying server into /etc/postfix/sasl_passwd:

mail.example.org pimedianas:MyVerySecretPwd

Last but not least, I redirected all the mail for root to my real email address in /etc/aliases:

root:   niccolo@example.org

Remember to compile all the files and restart the service:

postmap /etc/postfix/sasl_passwd
postmap /etc/postfix/sender_canonical_maps
newaliases
systemctl restart postfix.service

Now all the locally generated mails addressed to root, root@pimedianas, root@localhost or root@localhost.localdomain should have the MAIL FROM rewritten as above and forwarded to the external mailbox.