PostFix as a mail relay Ubuntu 14 LTS


This took some time, so i’d thought I might share it. If you have any improvements or comments, feel free to contribute.

The scenario, we have multiple post-fix mail relay servers sitting behind various ISP’s in various clouds or data-centers, they all point to a single (cluster) of mail servers (Zimbra of course). It took some time to get these MX’s to do the right thing with SMTP / TLS and SASL.

The MX sits behind a firewall on a private ip (172.16.1.25) (VyOS) which publishes TCP 25 and 465 for the communications.

First apt-get install postfix on a clean Ubuntu 14 LTS server, set it up as a satellite when dpkg-configure asks you to.

Then fetch the TLS and SASL dependencies

apt-get install  sasl2-bin postfix-tls sasl2-bin libsasl2-modules

For some odd reason, the socket links in /run between sasl authd and postfix don’t add up. A mess of security and other oddness. So in a quick and dirty way we fix this on reboot in a script called /etc/postfix/fixlink.sh

rm -r /var/run/saslauthd/
mkdir -p /var/spool/postfix/var/run/saslauthd
ln -s /var/spool/postfix/var/run/saslauthd /var/run
chgrp sasl /var/spool/postfix/var/run/saslauthd
service postfix restart
/etc/init.d/saslauthd start

To get Postfix to use the plain login for SASL configure the file /etc/postfix/sasl/smtpd.conf

pwcheck_method: saslauthd
mech_list: plain login

You can find some more details on the how and why here

Now for the Meat and Potatoes, the /etc/postfix/main.cf file:

inet_interfaces = all
myhostname = mx01.yourdomain.com
mynetworks = 192.168.0.0/16, 127.0.0.1, 172.16.1.26
myorigin = mydomain.com
mydestination =
smtpd_banner = $myhostname ESMTP
smtpd_use_tls = yes
smtp_use_tls = yes
smtp_enforce_tls = no
# TLS parameters
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtp_tls_note_starttls_offer = yes
smtpd_tls_loglevel=2
smtpd_tls_auth_only = yes
smtpd_tls_security_level = may
smtpd_tls_cert_file=/etc/postfix/commercial.crt
smtpd_tls_key_file=/etc/postfix/commercial.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_tls_exclude_ciphers = aNULL, DES, 3DES, MD5, DES+MD5, RC4, RC4-MD5
smtpd_tls_received_header = yes
tls_random_source = dev:/dev/urandom
# Sasl
smtpd_sasl_path = smtpd
smtpd_sasl_security_options = noanonymous
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
broken_sasl_auth_clients = yes
# Limits
default_process_limit = 100
smtpd_client_connection_count_limit = 10
smtpd_client_connection_rate_limit = 30
queue_minfree = 20971520
header_size_limit = 51200
message_size_limit = 10485760
smtpd_recipient_limit = 100
local_recipient_maps =
local_transport = error:no local delivery
parent_domain_matches_subdomains = debug_peer_list smtpd_access_maps
relay_domains = domain1.com domain2.com and some more domains
smtpd_recipient_restrictions =
 permit_sasl_authenticated,
 permit_mynetworks,
 reject_unauth_destination,
 reject_unverified_recipient
address_verify_negative_cache = no
unverified_recipient_reject_code = 550
maximal_queue_lifetime = 21d
relayhost = [your.mail.cluster.local]

Change the bold where appropriate of course

As you can see we use some SSL certs, these come from our own private CA, but you can use some self signed ones as well, just remember to cat the authorizing CA certificate into the CRT and have no password in your key. A lengthy explanation on the how and what can me found here

Now the /etc/postfix/master.cf, un-comment (or add) the bold lines and if all is equal, it should work…

#
# Postfix master process configuration file. For details on the format
# of the file, see the master(5) manual page (command: "man 5 master" or
# on-line: http://www.postfix.org/master.5.html).
#
# Do not forget to execute "postfix reload" after editing this file.
#
# ==========================================================================
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (yes) (never) (100)
# ==========================================================================
smtp inet n - - - - smtpd
#smtp inet n - - - 1 postscreen
#smtpd pass - - - - - smtpd
#dnsblog unix - - - - 0 dnsblog
#tlsproxy unix - - - - 0 tlsproxy
submission inet 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=$mua_sender_restrictions
# -o smtpd_recipient_restrictions=
 -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
 -o milter_macro_daemon_name=ORIGINATING
smtps inet n - - - - smtpd
# -o syslog_name=postfix/smtps
 -o smtpd_tls_wrappermode=yes
 -o smtpd_sasl_auth_enable=yes
# -o smtpd_reject_unlisted_recipient=no
# -o smtpd_client_restrictions=$mua_client_restrictions
# -o smtpd_helo_restrictions=$mua_helo_restrictions
# -o smtpd_sender_restrictions=$mua_sender_restrictions
# -o smtpd_recipient_restrictions=
 -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
 -o milter_macro_daemon_name=ORIGINATING
#628 inet n - - - - qmqpd
pickup unix n - - 60 1 pickup
cleanup unix n - - - 0 cleanup
qmgr unix n - n 300 1 qmgr
#qmgr unix n - n 300 1 oqmgr
tlsmgr unix - - - 1000? 1 tlsmgr
rewrite unix - - - - - trivial-rewrite
bounce unix - - - - 0 bounce
defer unix - - - - 0 bounce
trace unix - - - - 0 bounce
verify unix - - - - 1 verify
flush unix n - - 1000? 0 flush
proxymap unix - - n - - proxymap
proxywrite unix - - n - 1 proxymap
smtp unix - - - - - smtp
relay unix - - - - - smtp
# -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq unix n - - - - showq
error unix - - - - - error
retry unix - - - - - error
discard unix - - - - - discard
#local unix - n n - - local
virtual unix - n n - - virtual
lmtp unix - - - - - lmtp
anvil unix - - - - 1 anvil
scache unix - - - - 1 scache
#
# ====================================================================
# Interfaces to non-Postfix software. Be sure to examine the manual
# pages of the non-Postfix software to find out what options it wants.
#
# Many of the following services use the Postfix pipe(8) delivery
# agent. See the pipe(8) man page for information about ${recipient}
# and other message envelope options.
# ====================================================================
#
# maildrop. See the Postfix MAILDROP_README file for details.
# Also specify in main.cf: maildrop_destination_recipient_limit=1
#
maildrop unix - n n - - pipe
 flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${recipient}
#
# ====================================================================
#
# Recent Cyrus versions can use the existing "lmtp" master.cf entry.
#
# Specify in cyrus.conf:
# lmtp cmd="lmtpd -a" listen="localhost:lmtp" proto=tcp4
#
# Specify in main.cf one or more of the following:
# mailbox_transport = lmtp:inet:localhost
# virtual_transport = lmtp:inet:localhost
#
# ====================================================================
#
# Cyrus 2.1.5 (Amos Gouaux)
# Also specify in main.cf: cyrus_destination_recipient_limit=1
#
#cyrus unix - n n - - pipe
# user=cyrus argv=/cyrus/bin/deliver -e -r ${sender} -m ${extension} ${user}
#
# ====================================================================
# Old example of delivery via Cyrus.
#
#old-cyrus unix - n n - - pipe
# flags=R user=cyrus argv=/cyrus/bin/deliver -e -m ${extension} ${user}
#
# ====================================================================
#
# See the Postfix UUCP_README file for configuration details.
#
uucp unix - n n - - pipe
 flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
#
# Other external delivery methods.
#
ifmail unix - n n - - pipe
 flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)
bsmtp unix - n n - - pipe
 flags=Fq. user=bsmtp argv=/usr/lib/bsmtp/bsmtp -t$nexthop -f$sender $recipient
scalemail-backend unix - n n - 2 pipe
 flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store ${nexthop} ${user} ${extension}
mailman unix - n n - - pipe
 flags=FR user=list argv=/usr/lib/mailman/bin/postfix-to-mailman.py
 ${nexthop} ${user}

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