# Postfix

Related articles

- PostFix Howto With SASL
- Amavis
- Virtual user mail system
- Courier MTA
- Exim
- OpenSMTPD

From Postfix's site:

  Postfix attempts to be fast, easy to administer, and secure, while at the same time being sendmail compatible enough to not upset existing users. Thus, the outside has a sendmail-ish flavor, but the inside is completely different.

The goal of this article is to setup Postfix and explain what the basic configuration files do. There are instructions for setting up local system user-only delivery and a link to a guide for virtual user delivery.

## Installation

Install the postfix and openssl packages.

### DNS records

An MX record should point to the mail host. Usually this is done from configuration interface of your domain provider.

A mail exchanger record (MX record) is a type of resource record in the Domain Name System that specifies a mail server responsible for accepting email messages on behalf of a recipient's domain.

When an e-mail message is sent through the Internet, the sending mail transfer agent queries the Domain Name System for MX records of each recipient's domain name. This query returns a list of host names of mail exchange servers accepting incoming mail for that domain and their preferences. The sending agent then attempts to establish an SMTP connection to one of these servers, starting with the one with the smallest preference number, delivering the message to the first server with which a connection can be made.

Note: Some mail servers will not deliver mail to you if your MX record points to a CNAME. For best results, always point an MX record to an A record definition. For more information, see e.g. Wikipedia's List of DNS Record Types.

## Configuration

### master.cf

`/etc/postfix/master.cf` is the master configuration file where you can specify what kinds of protocols you will serve. It is also the place where you can put your new pipes e.g. to check for Spam!

It is recommended to enable secure SMTP as described in #Secure SMTP.

### main.cf

`/etc/postfix/main.cf` is the main configuration file where everything is configured. The settings below are recommended for virtual local-only delivery.

- `myhostname` should be set if your mail server has multiple domains, and you do not want the primary domain to be the mail host. You should have both a DNS A record and an MX record point to this hostname.

      myhostname = mail.nospam.net

- `mydomain` is usually the value of `myhostname`, minus the first part. If your domain is wonky, then just set it manually.

      mydomain = nospam.net

- `myorigin` is where the email will be seen as being sent from. I usually set this to the value of `mydomain`. For simple servers, this works fine. This is for mail originating from a local account. Since we are not doing local delivery (except sending), then this is not really as important as it normally would be.

      myorigin = $mydomain

- `mydestination` is the lookup for local users.

      mydestination = $myhostname, localhost.$mydomain, localhost

- `mynetworks` and `mynetwork_style` control relaying, and whom is allowed to. We do not want any relaying.

  For our sakes, we will simply set `mynetwork_style` to host, as we are trying to make a standalone Postfix host, that people will use webmail on. No relaying, no other MTA's. Just webmail.

      mynetworks_style = host

- `relaydomains` controls the destinations that Postfix will relay TO. The default value is $mydestination. This should be fine for now.

      relay_domains = $mydestination

- `home_mailbox` or `mail_spool_directory` control how mail is delivered/stored for the users.

  If set, `mail_spool_directory` specifies an absolute path where mail gets delivered. By default Postfix stores mails in `/var/spool/mail`.

      home_spool_directory = /home/vmailer

  Alternatively, if set, `home_mailbox` specifies a mailbox relative to the user's home directory where mail gets delivered (eg: /home/vmailer).

  Courier-IMAP requires "Maildir" format, so you must set it like the following example with trailing slash:

      home_mailbox = Maildir/

Warning: If you plan on implementing SSL/TLS, please respond safely to POODLE and FREAK/Logjam by adding the following to your configuration:

    smtpd_tls_mandatory_protocols=!SSLv2,!SSLv3
    smtp_tls_mandatory_protocols=!SSLv2,!SSLv3
    smtpd_tls_protocols=!SSLv2,!SSLv3
    smtp_tls_protocols=!SSLv2,!SSLv3
    smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK, aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CDC3-SHA, KRB5-DE5, CBC3-SHA

Then, generate a dhparam file by following these instructions and then adding the following to your configuration:

    smtpd_tls_dh1024_param_file = ${config_directory}/dhparams.pem

#### Default message and mailbox size limits

Postfix imposes both message and mailbox size limits by default. The message_size_limit controls the maximum size in bytes of a message, including envelope information. (default 10240000) The mailbox_size_limit controls the maximum size of any local individual mailbox or maildir file. This limits the size of any file that is written to upon local delivery, including files written by external commands (i.e. procmail) that are executed by the local delivery agent. (default is 51200000, set to 0 for no limit) If bounced message notifications are generated, check the size of the local mailbox under `/var/spool/mail` and use postconf to check these size limits:

    # postconf -d mailbox_size_limit
    mailbox_size_limit = 51200000
    # postconf -d message_size_limit
    message_size_limit = 10240000

### aliases

You can specify aliases (also known as forwarders) in `/etc/postfix/aliases`.

You need to map all mail addressed to root to another account since it is not a good idea to read mail as root.

Uncomment the following line, and change `you` to a real account.

    root: you

Once you have finished editing `/etc/postfix/aliases` you must run the postalias command:

    postalias /etc/postfix/aliases

For later changes you can use:

    newaliases

Tip: Alternatively you can create the file `~/.forward`, e.g. `/root/.forward` for root. Specify the user to whom root mail should be forwarded, e.g. user@localhost.

    /root/.forward

    user@localhost

## Local mail

To only deliver mail to local system users (that are in `/etc/passwd`), you only need to change the following lines in `/etc/postfix/main.cf`. Uncomment them and modify them to the specifics listed below. Everything else can be left as installed.

    mydestination = $myhostname, localhost.$mydomain, localhost
    inet_interfaces = loopback-only
    mynetworks_style = host
    append_dot_mydomain = no
    default_transport = error: Local delivery only!

## Virtual mail

Virtual mail is mail that does not map to a user account (`/etc/passwd`).

See Virtual user mail system for a comprehensive guide how to set it up.

## Postfix check

Run the `postfix check` command. It should output anything that you might have done wrong in a config file.

To see all of your configs, type `postconf`. To see how you differ from the defaults, try `postconf -n`.

## Start and test Postfix

Start/enable `postfix.service`.

Now lets see if Postfix is going to deliver mail for our test user.

    nc servername 25
    helo testmail.org
    mail from:<test@testmail.org>
    rcpt to:<cactus@virtualdomain.tld>
    data
    This is a test email.
    .
    quit

### Error response

    451 4.3.0 <lisi@test.com>:Temporary lookup failure

Maybe you have entered the wrong user/password for MySQL or the MySQL socket is not in the right place.

    550 5.1.1 <email@spam.me>: Recipient address rejected: User unknown in virtual mailbox table.

Double check content of mysql_virtual_mailboxes.cf and check the main.cf for mydestination

### See that you have received a email

Now type `$ find /home/vmailer`.

You should see something like the following:

    /home/vmailer/virtualdomain.tld/cactus@virtualdomain.tld
    /home/vmailer/virtualdomain.tld/cactus@virtualdomain.tld/tmp
    /home/vmailer/virtualdomain.tld/cactus@virtualdomain.tld/cur
    /home/vmailer/virtualdomain.tld/cactus@virtualdomain.tld/new
    /home/vmailer/virtualdomain.tld/cactus@virtualdomain.tld/new/1102974226.2704_0.bonk.testmail.org

The key is the last entry. This is an actual email, if you see that, it is working.

## Extra

### PostfixAdmin

To use PostfixAdmin, you need a working Apache/MySQL/PHP setup as described in Apache HTTP Server.

For IMAP functionality, you will need to install php-imap and uncomment imap.so in /etc/php/php.ini

Next, install postfixadmin.

This article or section needs language, wiki syntax or style improvements.

Reason: in-code comments (Discuss in Talk:Postfix#)

Edit the PostfixAdmin configuration file:

    /etc/webapps/postfixadmin/config.inc.php

    $CONF['configured'] = true;
    // correspond to dovecot maildir path /home/vmail/%d/%u
    $CONF['domain_path'] = 'YES';
    $CONF['domain_in_mailbox'] = 'YES';
    $CONF['database_type'] = 'mysql';
    $CONF['database_host'] = 'localhost';
    $CONF['database_user'] = 'postfix_user';
    $CONF['database_password'] = 'hunter2';
    $CONF['database_name'] = 'postfix_db';

    // globally change all instances of ''change-this-to-your.domain.tld''
    // to an appropriate value

If installing dovecot and you changed the password scheme in dovecot (to SHA512-CRYPT for example), reflect that with postfix

    /etc/webapps/postfixadmin/config.inc.php

    $CONF['encrypt'] = 'dovecot:SHA512-CRYPT';

Create the Apache configuration file:

    /etc/httpd/conf/extra/httpd-postfixadmin.conf

    Alias /postfixadmin "/usr/share/webapps/postfixAdmin"
    <Directory "/usr/share/webapps/postfixAdmin">
        DirectoryIndex index.html index.php
        AllowOverride All
        Options FollowSymlinks
        Require all granted
    </Directory>

And include it in `/etc/httpd/conf/httpd.conf`:

    # PostfixAdmin configuration
    Include conf/extra/httpd-postfixadmin.conf

Note: If you go to yourdomain/postfixadmin/setup.php and it says do not find config.inc.php, add `/etc/webapps/postfixadmin` to the `open_basedir` line in `/etc/php/php.ini`.
Note: If you get a blank page check the syntax of the file with `php -l /etc/webapps/postfixadmin/config.inc.php`.

### Secure SMTP

#### STARTTLS over SMTP (port 587)

To enable STARTTLS over SMTP (port 587, the proper way of securing SMTP), uncomment these lines in

    /etc/postfix/master.cf

    smtp      inet  n       -       n       -       -       smtpd
    submission inet n       -       n       -       -       smtpd
      -o smtpd_tls_security_level=encrypt
      -o smtpd_sasl_auth_enable=yes

If you need support for the deprecated SMTPS port 465, read the next section.

#### SMTPS (port 465)

The deprecated method of securing SMPT is using the wrapper mode which uses the system service smtps as a non-standard service and runs on port 465.

To enable it uncomment the following lines in

    /etc/postfix/master.cf

    smtps     inet  n       -       n       -       -       smtpd
      -o smtpd_tls_wrappermode=yes
      -o smtpd_sasl_auth_enable=yes

And verify that these lines are in `/etc/services`:

    smtps 465/tcp # Secure SMTP
    smtps 465/udp # Secure SMTP

If they are not there, go ahead and add them (replace the other listing for port 465). Otherwise Postfix will not start and you will get the following error:

    postfix/master[5309]: fatal: 0.0.0.0:smtps: Servname not supported for ai_socktype

### SpamAssassin

Note: The spamd user and group are created by default (with UID/GID 182) and do not require change. To start the server with default values, simply import the GnuPG Key, run sa-update and then start spamassassin.

Go over `/etc/mail/spamassassin/local.cf` and configure it to your needs.

Create an user and group for SpamAssassin.

    # groupadd -g 5001 spamd
    # useradd -u 5001 -g spamd -s /sbin/nologin -d /var/lib/spamassassin -m spamd
    # chown -R spamd:spamd /var/lib/spamassassin /etc/mail/spamassassin

To leave the service ready to run, let us update the SpamAssassin matching patterns. The GnuPG key Key fingerprint is 5E54 1DC9 59CB 8BAC 7C78 DFDC 4056 A61A 5244 EC45 and unfortunately is not signed by many, still, you need it.

    # sudo -u spamd -s
    $ curl http://spamassassin.apache.org/updates/GPG.KEY | sa-update --import -
    $ sa-update

Note: If you want to combine Spamassassin and Dovecot Mail Filtering you have to ignore the next two lines and continue further down instead.

Edit /etc/postfix/master.cf and add the content filter under smtp.

    smtp       inet  n       -       n       -       -       smtpd
           -o content_filter=spamassassin

Also add the following service entry for spamassassin

    spamassassin   unix   -     n       n      -       -       pipe
           user=spamd argv=/usr/bin/vendor_perl/spamc -f -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}

Now you can start `spamassassin.service`.

#### SpamAssassin combined with Dovecot LDA / Sieve (Mailfiltering)

Set up LDA and the Sieve-Plugin as described in Dovecot#Sieve. But ignore the last line `mailbox_command...` .

Instead add a pipe in `/etc/postfix/master.cf`:

     dovecot   unix  -       n       n       -       -       pipe
           flags=DRhu user=vmail:vmail argv=/usr/bin/vendor_perl/spamc -f -u spamd -e /usr/lib/dovecot/dovecot-lda -f ${sender} -d ${recipient}

And activate it in `/etc/postfix/main.cf`:

     virtual_transport = dovecot

#### SpamAssassin combined with Dovecot LMTP / Siege

Set up the LMTP and Siege as described in Dovecot#Sieve.

Edit `/etc/dovecot/conf.d/90-sieve.conf` and add:

     sieve_before = /etc/dovecot/sieve.d/
     sieve_extensions = +vnd.dovecot.filter
     sieve_plugins = sieve_extprograms

Create the directory:

     # mkdir /etc/dovecot/sieve.d/

Create a new file, `/etc/dovecot/sieve.d/spamassassin.sieve` which contains:

     require [ "vnd.dovecot.filter" ];
     filter "spamc" [ "--no-safe-fallback" ];

Compile the sieve rules `spamassassin.svbin`:

     # cd /etc/dovecot/sieve.d
     # sievec spamassassin.sieve

Finally, restart `dovecot.service`.

### Using Razor

Make sure you have installed SpamAssassin first, then:

Install the razor package.

Register with Razor.

     # sudo -u spamd -s
     $ mkdir /etc/mail/spamassassin/razor
     $ razor-admin -home=/etc/mail/spamassassin/razor -register
     $ razor-admin -home=/etc/mail/spamassassin/razor -create
     $ razor-admin -home=/etc/mail/spamassassin/razor -discover

Tell SpamAssassin about Razor, add

     razor_config /etc/mail/spamassassin/razor/razor-agent.conf

to `/etc/mail/spamassassin/local.cf`.

Tell Razor about itself, add

     razorhome = /etc/mail/spamassassin/razor/

to `/etc/mail/spamassassin/razor/razor-agent.conf`

Finally, restart `spamassassin.service`.

### Hide the sender's IP and user agent in the Received header

This is a privacy concern mostly, if you use Thunderbird and send an email. The received header will contain your LAN and WAN IP and info about the email client you used. (Original source: AskUbuntu) What we want to do is remove the Received header from outgoing emails. This can be done by the following steps:

Add this line to main.cf

    smtp_header_checks = regexp:/etc/postfix/smtp_header_checks

Create /etc/postfix/smtp_header_checks with this content:

    /^Received: .*/     IGNORE
    /^User-Agent: .*/   IGNORE

Finally, restart postfix.service

## See also

- Out of Office for Squirrelmail
- Postfix Ubuntu documentation
- Use Gmail as an SMTP relay

Category:

- Mail server