Postfix with SASL - ArchWiki

# Postfix with SASL

From ArchWiki

Related articles

- Postfix
- Dovecot

From Postfix's site:

  People who go to the trouble of installing Postfix may have the expectation that Postfix is more secure than some other mailers. The Cyrus SASL library contains a lot of code. With this, Postfix becomes as secure as other mail systems that use the Cyrus SASL library. Dovecot provides an alternative that may be worth considering.

## Introduction

In this article you will learn how to setup SASL authentication for Postfix.

Once Postfix is up and running you can add SASL authentication to avoid relaying. Only authenticated and trusted users will be able to send emails. This will avoid anonymous users to make spamming.

Since postfix package in [extra] is already compiled with SASL support, to enable SASL authentication you have two choices:

- Use cyrus-sasl package.
- Or enable your already configured Dovecot to handle Postfix authentication (as well as its own).

## Configuration with cyrus-sasl package

Install the cyrus-sasl package.

To enable SASL for accepting mail from other users, open the "Message submission" port (TCP 587) in `/etc/postfix/master.cf`, by uncommenting these lines (which are there by default, just commented):

    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_client_restrictions=$mua_client_restrictions
    #  -o smtpd_helo_restrictions=$mua_helo_restrictions
    #  -o smtpd_sender_restrictions=$mua_sender_restrictions
      -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject
      -o milter_macro_daemon_name=ORIGINATING

Note that this also enables SSL, so if you do not have a SSL certificate, keep the "smtpd_tls_security_level" option commented out.

The three restriction options (client, helo, sender) can also be left commented out, since smtpd_recipient_restrictions already handles SASL users.

SASL can use different authentication methods. The default one is PAM (as configured in `/etc/conf.d/saslauthd`), but to set it up properly you have to create `/etc/sasl2/smtpd.conf`:

    pwcheck_method: saslauthd
    mech_list: PLAIN LOGIN
    log_level: 7

Start/enable the `saslauthd.service`.

Restart the `postfix.service`.

Hopefully you should be able to telnet to your Postfix server with:

`telnet localhost 587`

You should then type:

`EHLO test.com`

This is roughly what you should see:

    Trying 127.0.0.1...

    Connected to localhost.localdomain
    Escape character is '^]'

    220 justin ESMTP Postfix
    EHLO test.com
    250-justin
    250-PIPELINING
    250-SIZE 10240000
    250-VRFY
    250-ETRN
    250-AUTH PLAIN OTP DIGEST-MD5 CRAM-MD5
    250 8BITMIME

## Configuration with Dovecot

If you are using Dovecot as your IMAP or POP mail server and your users already authenticate (with PAM maybe), then there is no need to configure another package.

Simply edit `/etc/postfix/master.cf` and add the following lines under the `submission` or `smtp` section (depending on what you are using):

      # SASL authentication with dovecot
      -o smtpd_tls_security_level=encrypt
      -o smtpd_sasl_auth_enable=yes
      -o smtpd_sasl_type=dovecot
      -o smtpd_sasl_path=private/auth
      -o smtpd_sasl_security_options=noanonymous
      -o smtpd_sasl_local_domain=$myhostname
      -o smtpd_client_restrictions=permit_sasl_authenticated,reject
      -o smtpd_recipient_restrictions=reject_non_fqdn_recipient,reject_unknown_recipient_domain,permit_sasl_authenticated,reject

Using this configuration implies that only authenticated users can send mails. You can see this from `smtpd_client_restrictions` option.

Now add the following to Dovecot configuration file in `/etc/dovecot/dovecot.conf`:

    service auth {
      unix_listener /var/spool/postfix/private/auth {
        group = postfix
        mode = 0660
        user = postfix
      }
      user = root
    }

As you can see a unix socket is created in `/var/spool/postfix/private/auth`, the same specified in `smtpd_sasl_path` option of `master.cf`

Finally restart both postfix and dovecot services.

## See also

- Postfix SASL readme in Postfix official documentation.

- SASL authentication with Dovecot in Dovecot official documentation.

- Centos Howto Postfix SASL

Category:

- Mail server