content/blog/mail_server_alpine_postfix_dovecot_tutorial.md: finish postfix section

content/blog/mail_server_alpine_postfix_dovecot_tutorial.md

@@ -112,7 +112,7 @@ choice.
 An MX record denotes that your domain is used to send and receive email, and tells other MTAs the domain name of your
 mail server. We will use `mail.domain.com` for your MX record. For instance, my MX record looks like:
 
-```dns-zone
+```bindzone
 revsuine.xyz.                    14400 IN MX    0 mail.revsuine.xyz
 ```
 
@@ -124,19 +124,19 @@ same as the IP address of `domain.com`, or an A record if the IP address is not
 
 I use a CNAME record because the IP addresses of `mail.revsuine.xyz` and `revsuine.xyz` are the same, so my record is:
 
-```dns-zone
+```bindzone
 mail.revsuine.xyz.               14400 IN CNAME revsuine.xyz
 ```
 
 If you use an A record, your record may look something like
 
-```dns-zone
+```bindzone
 mail.domain.com.                    14400 IN A     ip.address.here
 ```
 
 If you use IPv6, you should also add an AAAA record, e.g.:
 
-```dns-zone
+```bindzone
 mail.domain.com.                    14400 IN AAAA  ip:address:here::
 ```
 
@@ -178,3 +178,97 @@ following TCP ports are open on your firewall:
 
 # Postfix
 
+Postfix is a [mail transport agent](https://en.wikipedia.org/wiki/Message_transfer_agent) (aka SMTP server). [In its
+own words](https://www.postfix.org/):
+
+> Postfix attempts to be fast, easy to administer, and secure. The outside has a definite Sendmail-ish flavor, but the
+> inside is completely different.
+
+## Installing Postfix
+
+On your server, install Postfix with:
+
+    # apk add postfix
+
+You likely also want to have Postfix documentation:
+
+    # apk add postfix-doc
+
+Verify that Postfix is installed by checking its version:
+
+    $ postconf mail_version
+
+## Configuring Postfix
+
+Edit `/etc/postfix/main.cf`.
+
+You should set `myhostname` to the hostname of your server; [in my case, this is
+`master.revsuine.xyz`](### A note on my DNS records).
+
+Now set `mydomain` to the domain you intend to send email from. For instance, my email addresses are
+`name@revsuine.xyz`, so `mydomain` is set to `revsuine.xyz`.
+
+`myorigin` determines the domain name in the `From:` field of locally sent emails. So you could for instance set this
+to `revsuine.xyz`.
+
+`maillog_file` denotes where Postfix's log file is. By default this is `/var/log/messages`; you may want to configure
+Postfix to have a dedicated log file like `/var/log/postfix.log`.
+
+You probably want to have `logrotate` rotate your Postfix log. If there isn't already such a file, you want to create
+one at `/etc/logrotate.d/postfix`:
+
+```
+/var/log/postfix*.log
+/var/log/mail*.log
+{
+    daily
+    missingok
+    notifempty
+    rotate 7
+}
+```
+
+## Send your first email
+
+Have the `postfix` service auto-start upon boot, and start it during this session:
+
+    # rc-update add postfix default
+    # rc-service postfix start
+
+You can now send an email with the following command:
+
+    $ echo "test email" | sendmail user@externaldomain.com
+
+Send this email to your email account with an external server, e.g. a gmail account. Note that Protonmail has quite
+stringent spam filters and this likely would be rejected by Protonmail, i.e. not even reach your spam folder.
+
+## Configure email aliases
+
+You can configure aliases for your mail server. Edit the `/etc/postfix/aliases`[^postfix_aliases_location] file.
+
+You shouldn't receive mail as root, so configure `root` to have an alias to your user, e.g.
+
+```
+root: revsuine
+```
+
+You also *must* have a `MAILER-DAEMON` and `postmaster` alias present:
+
+```
+MAILER-DAEMON: postmaster
+postmaster:    root
+```
+
+Note how you can have referential aliases; mail to `postmaster` is aliased to `root`, which is aliased to `revsuine`,
+so ultimately `revsuine` will get `postmaster`'s mail.
+
+You can continue to populate the aliases file with whatever aliases you want.
+
+<!-- FOOTNOTES: -->
+
+[^postfix_aliases_location]: Your aliases file will most likely be in this location by default, but you can run
+
+        $ postconf alias_maps
+
+    to find out where this file should be.
+