Introduction

Postfix is a Mail Transfer Agent (MTA) which is the default MTA for Ubuntu. It is in Ubuntu's main repository, which means that it receives security updates. This guide explains how to install and configure postfix and set it up as an SMTP server using a secure connection.

Installation

In order to install Postfix with SMTP-AUTH and TLS do the following steps:

apt-get install postfix postfix-tls

Configuration

Run:

dpkg-reconfigure postfix

Insert the following details when asked (replacing server1.example.com with your domain name if you have one):

• Internet Site
• NONE
• server1.example.com
• server1.example.com, localhost.example.com, localhost
• No
• 127.0.0.0/8
• 0
• +

Then run the following commands:

postconf -e 'smtpd_sasl_local_domain ='
postconf -e 'smtpd_sasl_auth_enable = yes'
postconf -e 'smtpd_sasl_security_options = noanonymous'
postconf -e 'broken_sasl_auth_clients = yes'
postconf -e 'smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination'
postconf -e 'inet_interfaces = all'
echo 'pwcheck_method: saslauthd' >> /etc/postfix/sasl/smtpd.conf
echo 'mech_list: plain login' >> /etc/postfix/sasl/smtpd.conf

mkdir /etc/postfix/ssl
cd /etc/postfix/ssl/
openssl genrsa -des3 -rand /etc/hosts -out smtpd.key 1024
chmod 600 smtpd.key
openssl req -new -key smtpd.key -out smtpd.csr
openssl x509 -req -days 3650 -in smtpd.csr -signkey smtpd.key -out smtpd.crt
openssl rsa -in smtpd.key -out smtpd.key.unencrypted
mv -f smtpd.key.unencrypted smtpd.key
openssl req -new -x509 -extensions v3_ca -keyout cakey.pem -out cacert.pem -days 3650

postconf -e 'smtpd_tls_auth_only = no'
postconf -e 'smtp_use_tls = yes'
postconf -e 'smtpd_use_tls = yes'
postconf -e 'smtp_tls_note_starttls_offer = yes'
postconf -e 'smtpd_tls_key_file = /etc/postfix/ssl/smtpd.key'
postconf -e 'smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.crt'
postconf -e 'smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem'
postconf -e 'smtpd_tls_loglevel = 1'
postconf -e 'smtpd_tls_received_header = yes'
postconf -e 'smtpd_tls_session_cache_timeout = 3600s'
postconf -e 'tls_random_source = dev:/dev/urandom'
postconf -e 'myhostname = server1.example.com'

The file /etc/postfix/main.cf should now look like this:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

myhostname = server1.example.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = server1.example.com, localhost.example.com, localhost
relayhost =
mynetworks = 127.0.0.0/8
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
smtpd_sasl_local_domain =
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject _unauth_destination
smtpd_tls_auth_only = no
smtp_use_tls = yes
smtpd_use_tls = yes
smtp_tls_note_starttls_offer = yes
smtpd_tls_key_file = /etc/postfix/ssl/smtpd.key
smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.crt
smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom

Restart the postfix daemon like this:

/etc/init.d/postfix restart

Authentication

Authentication will be done by saslauthd. To install it, type:

apt-get install libsasl2 sasl2-bin libsasl2-modules libdb3-util procmail

We have to change a few things to make it work properly. Because Postfix runs chrooted in /var/spool/postfix we have to do the following:

mkdir -p /var/spool/postfix/var/run/saslauthd
rm -fr /var/run/saslauthd

Now we have to edit /etc/default/saslauthd in order to activate saslauthd. Remove # in front of START=yes and add the line PARAMS="-m /var/spool/postfix/var/run/saslauthd":

# This needs to be uncommented before saslauthd will be run automatically
START=yes

PARAMS="-m /var/spool/postfix/var/run/saslauthd"

# You must specify the authentication mechanisms you wish to use.
# This defaults to "pam" for PAM support, but may also include
# "shadow" or "sasldb", like this:
# MECHANISMS="pam shadow"

MECHANISMS="pam"

Finally we have to edit /etc/init.d/saslauthd. Change the line

dir=`dpkg-statoverride --list $PWDIR`

to

#dir=`dpkg-statoverride --list $PWDIR`

Then change the variables PWDIR and PIDFILE and add the variable dir at the beginning of the file:

PWDIR="/var/spool/postfix/var/run/${NAME}"
PIDFILE="${PWDIR}/saslauthd.pid"
dir="root sasl 755 ${PWDIR}"

Testing

Now start saslauthd:

/etc/init.d/saslauthd start

To see if SMTP-AUTH and TLS work properly now run the following command:

telnet localhost 25

After you have established the connection to your postfix mail server type

ehlo localhost

If you see the lines

250-STARTTLS
250-AUTH

among others, everything is working.

Type quit to return to the system's shell.

CategoryCleanup