====== Raspberry Pi NAS: The mail subsystem ======

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 **[[raspberrypi_nas]]**.

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:

<file>
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
</file>

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

<file>
root                       pimedianas@example.org
root@pimedianas            pimedianas@example.org
root@localhost             pimedianas@example.org
root@localhost.localdomain pimedianas@example.org
</file>

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

<file>
127.0.1.1  localhost.localdomain   localhost
</file>

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

<file>
mail.example.org pimedianas:MyVerySecretPwd
</file>

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

<file>
root:   niccolo@example.org
</file>

Remember to compile all the files and restart the service:

<code>
postmap /etc/postfix/sasl_passwd
postmap /etc/postfix/sender_canonical_maps
newaliases
systemctl restart postfix.service
</code>

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.