FreeBSD email server - Part 2: Mailing with Postfix

#Tutorial #FreeBSD #Email #Postfix

Welcome to the second part of my FreeBSD email server series. In this series, I will guide you through setting up your own email service. Be sure to done the preparations from part 1 of this series.

This part will guide you through setting up email service on your machine using Postfix. Basic installation is pretty straightforward, but there is a lot to configure. If you are not sure what some configuration options do, please read up on them. There is a lot to do wrong with a mail server, and doing things wrong will likely get you on a blacklist which will make other servers stop processing the mail you are trying to send out.

Setting up Postfix is one of the harder parts of configuring a mail server. If you have questions after reading the full guide, please find me on IRC. You can find details on how to do so on my homepage.

Installing Postfix

Installation procedures on FreeBSD are pretty straightforward. Unlike certbot from the previous part, we will need to compile Postfix from source in order to use PostgreSQL as a database back-end. Thanks to FreeBSD’s ports, this is not difficult either. If this is your first port to compile, you probably need to get the ports tree first. You can download and extract this using the following command.

{% highlight sh %} portsnap fetch extract {% endhighlight %}

Once that has finished running, go into the directory containing the build instructions for Postfix, and start the installation process.

{% highlight sh %} cd /usr/ports/mail/postfix make configure install {% endhighlight %}

This will open a pop up with a number of options you can enable or disable. The enabled defaults are fine, but you will have to enable the PGSQL option. This will allow you to use the configuration tables created in part 1.

Enabling Postfix

Enable the Postfix service for rcinit. This allows you to use service postfix start once configuration is done, and will auto start the service on system boot. In addition, the default mailer on FreeBSD, sendmail should be disabled so nothing is in Postfix’s way when trying to deal with processing email traffic.

{% highlight sh %}

disable the default sendmail system

echo ‘daily_clean_hoststat_enable=“NO”’ » /etc/periodic.conf.local echo ‘daily_status_mail_rejects_enable=“NO”’ » /etc/periodic.conf.local echo ‘daily_status_include_submit_mailq=“NO”’ » /etc/periodic.conf.local echo ‘daily_submit_queuerun=“NO”’ » /etc/periodic.conf.local echo ‘sendmail_enable=“NONE”’ » /etc/rc.conf.local

enable postfix

echo ‘postfix_enable=“YES”’ » /etc/rc.conf.local {% endhighlight %}

Configuring Postfix

There is a ton to configure for Postfix. This configuration happens in two files, main.cf and master.cf. Additionally, as some data is in the PostgreSQL database, three files with information on how to query for this information are needed. All of these files are in /usr/local/etc/postfix.

The guide has a comment line for most blocks. It is advised that if you decide to just copy and paste the contents, you copy that along so you have some sort of indication of what is where. This could help you out if you ever need to change anything later on.

main.cf

Compatibility

The configuration file starts off by setting the compatibility level. If postfix updates the configuration scheme and deprecates certain options, you will be notified of this in the logs.

{% highlight ini %}

compatibility

compatibility_level = 2 {% endhighlight %}

Directory paths

These options indicate where Postfix will look and keep certain files required for correct operation.

{% highlight ini %}

directory paths

queue_directory = /var/spool/postfix command_directory = /usr/local/sbin daemon_directory = /usr/local/libexec/postfix data_directory = /var/db/postfix {% endhighlight %}

Domain configuration

The domain configuration instruct the server of the domain(s) it should serve for. Use your FQDN without sub domains for mydomain. You can use a sub domain for myhostname, but you are not required to. The most common setting is using a mail sub domain for all mail related activities, which would result in something like this.

{% highlight ini %}

domain configuration

myhostname = mail.domain.tld mydomain = domain.tld myorigin = $mydomain {% endhighlight %}

Listening directives

All internet devices it should listen on, and all domains this server should consider itself the endpoint for, should be listed here. The defaults in the example block are good enough, as we put some of our data in the PostgreSQL database instead.

{% highlight ini %}

listening directives

inet_interfaces = all mydestination = $myhostname, localhost.$mydomain, localhost {% endhighlight %}

Reject unknown recipients

How to deal with messages sent to an email address whose domain points to your server’s address, but have no actual mailbox. A code of 550 means to inform the remote server that delivery is not possible and will not be possible. This should stop the remote server from trying it again.

{% highlight ini %}

reject unknown recipients

unknown_local_recipient_reject_code = 550 {% endhighlight %}

Trust

{% highlight ini %}

trust

mynetworks_style = host {% endhighlight %}

Address extensions

This block is optional. It allows you to use email address extensions. These are addresses with an additional character in them that will drop the email in the non extended address' mailbox, but allows you to quickly filter on them as the sent-to address contains the extension.

{% highlight ini %}

address extensions

recipient_delimiter = + {% endhighlight %}

Virtual domain directives

This part is where things get important. Virtual domains allow you to handle mail for a large number of domains that are different from the actual server’s domain. This is where the database configuration comes in to play. It is important to note the static:125 values. The 125 should map to the UID of the postfix user account on your system.

{% highlight ini %}

virtual domain directives

virtual_mailbox_base = /srv/mail virtual_mailbox_domains = pgsql:/usr/local/etc/postfix/pgsql-virtual-domains.cf virtual_mailbox_maps = pgsql:/usr/local/etc/postfix/pgsql-virtual-users.cf virtual_alias_maps = pgsql:/usr/local/etc/postfix/pgsql-virtual-aliases.cf virtual_uid_maps = static:125 virtual_gid_maps = static:125 virtual_transport = lmtp:unix:private/dovecot-lmtp {% endhighlight %}

TLS setup

The TLS setup configures your server to use secure connections. The keys used here have been generated in the previous part of this series.

{% highlight ini %}

TLS setup

smtpd_tls_cert_file = /usr/local/etc/letsencrypt/live/domain.tld/fullchain.pem smtpd_tls_key_file = /usr/local/etc/letsencrypt/live/domain.tld/privkey.pem smtpd_use_tls = yes smtpd_tls_auth_only = yes {% endhighlight %}

SASL setup

SASL deals with the authentication of the users to your email server.

{% highlight ini %}

SASL setup

smtpd_sasl_type = dovecot smtpd_sasl_path = private/auth smtpd_sasl_auth_enable = yes smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination smtpd_relay_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination {% endhighlight %}

Debugging

The debugging options are generally useful in case things break. If you have little traffic, you could leave them on forever in case you want to debug something later on. Once your server is working as intended, you should turn these options off. The postfix logs get pretty big in a short amount of time.

{% highlight ini %}

debugging

debug_peer_level = 2 debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/binary ddd $daemon_directory/$process_name $process_id & sleep 5 {% endhighlight %}

Installation time defaults

These options should not be touched, but are very important to have for your server.

{% highlight ini %}

install-time defaults

sendmail_path = /usr/local/sbin/sendmail newaliases_path = /usr/local/bin/newaliases mailq_path = /usr/local/bin/mailq setgid_group = maildrop html_directory = /usr/local/share/doc/postfix manpage_directory = /usr/local/man sample_directory = /usr/local/etc/postfix readme_directory = /usr/local/share/doc/postfix inet_protocols = ipv4 meta_directory = /usr/local/libexec/postfix shlib_directory = /usr/local/lib/postfix {% endhighlight %}

master.cf

For the master.cf file, you can use the following configuration block.

{% highlight cfg %} submission inet n - n - - smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_reject_unlisted_recipient=no -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject -o milter_macro_daemon_name=ORIGINATING pickup unix n - n 60 1 pickup cleanup unix n - n - 0 cleanup qmgr unix n - n 300 1 qmgr tlsmgr unix - - n 1000? 1 tlsmgr rewrite unix - - n - - trivial-rewrite bounce unix - - n - 0 bounce defer unix - - n - 0 bounce trace unix - - n - 0 bounce verify unix - - n - 1 verify flush unix n - n 1000? 0 flush proxymap unix - - n - - proxymap proxywrite unix - - n - 1 proxymap smtp unix - - n - - smtp relay unix - - n - - smtp showq unix n - n - - showq error unix - - n - - error retry unix - - n - - error discard unix - - n - - discard local unix - n n - - local virtual unix - n n - - virtual lmtp unix - - n - - lmtp anvil unix - - n - 1 anvil scache unix - - n - 1 scache {% endhighlight %}

SQL query files

The following three configuration files deal with the SQL query files to make Postfix able of getting some of its configuration from a database. You obviously have to change the first 4 directives to match your database authentication credentials.

pgsql-virtual-domains.cf

{% highlight ini %} user = postgres password = incredibly-secret! hosts = 127.1 dbname = mail query = SELECT 1 FROM domains WHERE name='%s'; {% endhighlight %}

pgsql-virtual-users.cf

{% highlight ini %} user = postgres password = incredibly-secret! hosts = 127.1 dbname = mail query = SELECT 1 FROM users WHERE local='%u' AND domain='%d'; {% endhighlight %}

pgsql-virtual-aliases.cf

{% highlight ini %} user = postfix password = nope hosts = 127.1 dbname = mail query = SELECT destination FROM aliases WHERE origin='%s'; {% endhighlight %}

Conclusion

This should be enough Postfix configuration, for now. Next part involves Dovecot, which will enable IMAP. It will also provide the SASL mechanism defined in this part.