Postfix
Introduction
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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 libsasl2 sasl2-bin libsasl2-modules libdb3-util procmail
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
- Yes
- 0
- +
- all
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 $mail_name (Ubuntu) biff = no # appending .domain is the MUA's job. append_dot_mydomain = no # Uncomment the next line to generate "delayed mail" warnings #delay_warning_time = 4h myhostname = server1.example.com alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases myorigin = /etc/mailname mydestination = server1.example.com, localhost.example.com, localhost relayhost = mynetworks = 127.0.0.0/8 mailbox_command = procmail -a "$EXTENSION" 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.
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"
Note: If you prefer, you can use "shadow" instead of "pam". This will use MD5 hashed password transfer and is perfectly secure. The username and password needed to authenticate will be those of the users on the system you are using on the server.
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.
Other Postfix Information
These guides will teach your howto setup Postfix mail servers from basic to advanced.
Postfix Basic Setup
[https://wiki.ubuntu.com/PostfixBasicSetupHowto Posfix Basic Setup Howto] will teach you the concepts of Posfix and how you can get Postfix basics setup up and running. If you are new to Postfix it is recomended to follow this guide first.
Postfix Virtual Mailbox and Antivirus Filtering
[https://wiki.ubuntu.com/PostfixVirtualMailBoxClamSmtpHowto Postfix Virtual MailBox ClamSmtp Howto] will teach you howto setup a Virtual mailboxes using non-linux accounts where each user will authenticate using their e-mail address with Dovecot POP3/IMAP server and ClamSMTP Antivirus to filter both incoming and out going mails for known viruses.
Postfix Complete Solution
[https://wiki.ubuntu.com/PostfixCompleteVirtualMailSystemHowto Postfix Complete Virtual Mail System Howto] will help you if you are managing a large number of virtual domains at an ISP level service provider or in a large corporation where you mange few hundred or thousand mail domains. This guide is appropriate if you are looking a complete solution with:
- Web based system administration
- Unlimited number of domains
- Virtual mail users without the need for shell accounts
- Domain specific user names
- Mailbox quotas
- Web access to email accounts
- Web base interface to change user passwords
- IMAP and POP3 support
- Auto responders
- SMTP Authentication for secure relaying
- SSL for transport layer security
- Strong SPAM filtering
- Anti-Virus filtering
- Log Analysis