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# Postfix (SMTP)
# --------------
# Postfix handles the transmission of email between servers
# using the SMTP protocol. It is a Mail Transfer Agent (MTA).
# Postfix listens on port 25 (SMTP) for incoming mail from
# other servers on the Internet. It is responsible for very
# basic email filtering such as by IP address and greylisting,
# it checks that the destination address is valid, rewrites
# destinations according to aliases, and passses email on to
# another service for local mail delivery.
# The first hop in local mail delivery is to Spamassassin via
# LMTP. Spamassassin then passes mail over to Dovecot for
# storage in the user's mailbox.
# Postfix also listens on ports 465/587 (SMTPS, SMTP+STARTLS) for
# connections from users who can authenticate and then sends
# their email out to the outside world. Postfix queries Dovecot
# to authenticate users.
# Address validation, alias rewriting, and user authentication
# is configured in a separate setup script
# because of the overlap of this part with the Dovecot
# configuration.
source setup/ # load our functions
source /etc/mailinabox.conf # load global vars
# ### Install packages.
# Install postfix's packages.
# * `postfix`: The SMTP server.
# * `postfix-pcre`: Enables header filtering.
# * `postgrey`: A mail policy service that soft-rejects mail the first time
# it is received. Spammers don't usually try agian. Legitimate mail
# always will.
# * `ca-certificates`: A trust store used to squelch postfix warnings about
# untrusted opportunistically-encrypted connections.
echo "Installing Postfix (SMTP server)..."
apt_install postfix postfix-sqlite postfix-pcre postgrey ca-certificates
# ### Basic Settings
# Set some basic settings...
# * Have postfix listen on all network interfaces.
# * Make outgoing connections on a particular interface (if multihomed) so that SPF passes on the receiving side.
# * Set our name (the Debian default seems to be "localhost" but make it our hostname).
# * Set the name of the local machine to localhost, which means xxx@localhost is delivered locally, although we don't use it.
# * Set the SMTP banner (which must have the hostname first, then anything).
tools/ /etc/postfix/ \
inet_interfaces=all \
smtp_bind_address=$PRIVATE_IP \
smtp_bind_address6=$PRIVATE_IPV6 \
smtpd_banner="\$myhostname ESMTP Hi, I'm a Mail-in-a-Box (Ubuntu/Postfix; see" \
# Tweak some queue settings:
# * Inform users when their e-mail delivery is delayed more than 3 hours (default is not to warn).
# * Stop trying to send an undeliverable e-mail after 2 days (instead of 5), and for bounce messages just try for 1 day.
tools/ /etc/postfix/ \
delay_warning_time=3h \
maximal_queue_lifetime=2d \
# ### Outgoing Mail
# Enable the 'submission' ports 465 and 587 and tweak their settings.
# * Enable authentication. It's disabled globally so that it is disabled on port 25,
# so we need to explicitly enable it here.
# * Do not add the OpenDMAC Authentication-Results header. That should only be added
# on incoming mail. Omit the OpenDMARC milter by re-setting smtpd_milters to the
# OpenDKIM milter only. See
# * Even though we dont allow auth over non-TLS connections (smtpd_tls_auth_only below, and without auth the client cant
# send outbound mail), don't allow non-TLS mail submission on this port anyway to prevent accidental misconfiguration.
# Setting smtpd_tls_security_level=encrypt also triggers the use of the 'mandatory' settings below (but this is ignored with smtpd_tls_wrappermode=yes.)
# * Give it a different name in syslog to distinguish it from the port 25 smtpd server.
# * Add a new cleanup service specific to the submission service ('authclean')
# that filters out privacy-sensitive headers on mail being sent out by
# authenticated users. By default Postfix also applies this to attached
# emails but we turn this off by setting nested_header_checks empty.
tools/ /etc/postfix/ -s -w \
"smtps=inet n - - - - smtpd
-o smtpd_tls_wrappermode=yes
-o smtpd_sasl_auth_enable=yes
-o syslog_name=postfix/submission
-o smtpd_milters=inet:
-o cleanup_service_name=authclean" \
"submission=inet n - - - - smtpd
-o smtpd_sasl_auth_enable=yes
-o syslog_name=postfix/submission
-o smtpd_milters=inet:
-o smtpd_tls_security_level=encrypt
-o cleanup_service_name=authclean" \
"authclean=unix n - - - 0 cleanup
-o header_checks=pcre:/etc/postfix/outgoing_mail_header_filters
-o nested_header_checks="
# Install the `outgoing_mail_header_filters` file required by the new 'authclean' service.
cp conf/postfix_outgoing_mail_header_filters /etc/postfix/outgoing_mail_header_filters
# Modify the `outgoing_mail_header_filters` file to use the local machine name and ip
# on the first received header line. This may help reduce the spam score of email by
# removing the reference.
sed -i "s/PRIMARY_HOSTNAME/$PRIMARY_HOSTNAME/" /etc/postfix/outgoing_mail_header_filters
sed -i "s/PUBLIC_IP/$PUBLIC_IP/" /etc/postfix/outgoing_mail_header_filters
# Enable TLS on incoming connections. It is not required on port 25, allowing for opportunistic
# encryption. On ports 465 and 587 it is mandatory (see above). Shared and non-shared settings are
# given here. Shared settings include:
# * Require TLS before a user is allowed to authenticate.
# * Set the path to the server TLS certificate and 2048-bit DH parameters for old DH ciphers.
# For port 25 only:
# * Disable extremely old versions of TLS and extremely unsafe ciphers, but some mail servers out in
# the world are very far behind and if we disable too much, they may not be able to use TLS and
# won't fall back to cleartext. So we don't disable too much. smtpd_tls_exclude_ciphers applies to
# both port 25 and port 587, but because we override the cipher list for both, it probably isn't used.
# Use Mozilla's "Old" recommendations at
tools/ /etc/postfix/ \
smtpd_tls_auth_only=yes \
smtpd_tls_cert_file=$STORAGE_ROOT/ssl/ssl_certificate.pem \
smtpd_tls_key_file=$STORAGE_ROOT/ssl/ssl_private_key.pem \
smtpd_tls_dh1024_param_file=$STORAGE_ROOT/ssl/dh2048.pem \
smtpd_tls_protocols="!SSLv2,!SSLv3" \
smtpd_tls_ciphers=medium \
smtpd_tls_exclude_ciphers=aNULL,RC4 \
tls_preempt_cipherlist=no \
# For ports 465/587 (via the 'mandatory' settings):
# * Use Mozilla's "Intermediate" TLS recommendations from
# using and overriding the "high" cipher list so we don't conflict with the more permissive settings for port 25.
tools/ /etc/postfix/ \
smtpd_tls_mandatory_protocols="!SSLv2,!SSLv3,!TLSv1,!TLSv1.1" \
smtpd_tls_mandatory_ciphers=high \
# Prevent non-authenticated users from sending mail that requires being
# relayed elsewhere. We don't want to be an "open relay". On outbound
# mail, require one of:
# * `permit_sasl_authenticated`: Authenticated users (i.e. on port 465/587).
# * `permit_mynetworks`: Mail that originates locally.
# * `reject_unauth_destination`: No one else. (Permits mail whose destination is local and rejects other mail.)
tools/ /etc/postfix/ \
# ### DANE
# When connecting to remote SMTP servers, prefer TLS and use DANE if available.
# Prefering ("opportunistic") TLS means Postfix will use TLS if the remote end
# offers it, otherwise it will transmit the message in the clear. Postfix will
# accept whatever SSL certificate the remote end provides. Opportunistic TLS
# protects against passive easvesdropping (but not man-in-the-middle attacks).
# Since we'd rather have poor encryption than none at all, we use Mozilla's
# "Old" recommendations at
# for opportunistic encryption but "Intermediate" recommendations when DANE
# is used (see next and above). The cipher lists are set above.
# DANE takes this a step further:
# Postfix queries DNS for the TLSA record on the destination MX host. If no TLSA records are found,
# then opportunistic TLS is used. Otherwise the server certificate must match the TLSA records
# or else the mail bounces. TLSA also requires DNSSEC on the MX host. Postfix doesn't do DNSSEC
# itself but assumes the system's nameserver does and reports DNSSEC status. Thus this also
# relies on our local DNS server (see and `smtp_dns_support_level=dnssec`.
# The `smtp_tls_CAfile` is superflous, but it eliminates warnings in the logs about untrusted certs,
# which we don't care about seeing because Postfix is doing opportunistic TLS anyway. Better to encrypt,
# even if we don't know if it's to the right party, than to not encrypt at all. Instead we'll
# now see notices about trusted certs. The CA file is provided by the package `ca-certificates`.
tools/ /etc/postfix/ \
smtp_tls_protocols=\!SSLv2,\!SSLv3 \
smtp_tls_ciphers=medium \
smtp_tls_exclude_ciphers=aNULL,RC4 \
smtp_tls_security_level=dane \
smtp_dns_support_level=dnssec \
smtp_tls_mandatory_protocols="!SSLv2,!SSLv3,!TLSv1,!TLSv1.1" \
smtp_tls_mandatory_ciphers=high \
smtp_tls_CAfile=/etc/ssl/certs/ca-certificates.crt \
# ### Incoming Mail
# Pass any incoming mail over to a local delivery agent. Spamassassin
# will act as the LDA agent at first. It is listening on port 10025
# with LMTP. Spamassassin will pass the mail over to Dovecot after.
# In a basic setup we would pass mail directly to Dovecot by setting
# virtual_transport to `lmtp:unix:private/dovecot-lmtp`.
tools/ /etc/postfix/ "virtual_transport=lmtp:[]:10025"
# Because of a spampd bug, limit the number of recipients in each connection.
# See
tools/ /etc/postfix/ lmtp_destination_recipient_limit=1
# Who can send mail to us? Some basic filters.
# * `reject_non_fqdn_sender`: Reject not-nice-looking return paths.
# * `reject_unknown_sender_domain`: Reject return paths with invalid domains.
# * `reject_authenticated_sender_login_mismatch`: Reject if mail FROM address does not match the client SASL login
# * `reject_rhsbl_sender`: Reject return paths that use blacklisted domains.
# * `permit_sasl_authenticated`: Authenticated users (i.e. on port 587) can skip further checks.
# * `permit_mynetworks`: Mail that originates locally can skip further checks.
# * `reject_rbl_client`: Reject connections from IP addresses blacklisted in
# * `reject_unlisted_recipient`: Although Postfix will reject mail to unknown recipients, it's nicer to reject such mail ahead of greylisting rather than after.
# * `check_policy_service`: Apply greylisting using postgrey.
# Notes: #NODOC
# permit_dnswl_client can pass through mail from whitelisted IP addresses, which would be good to put before greylisting #NODOC
# so these IPs get mail delivered quickly. But when an IP is not listed in the permit_dnswl_client list (i.e. it is not #NODOC
# whitelisted) then postfix does a DEFER_IF_REJECT, which results in all "unknown user" sorts of messages turning into #NODOC
# "450 4.7.1 Client host rejected: Service unavailable". This is a retry code, so the mail doesn't properly bounce. #NODOC
tools/ /etc/postfix/ \
smtpd_sender_restrictions="reject_non_fqdn_sender,reject_unknown_sender_domain,reject_authenticated_sender_login_mismatch,reject_rhsbl_sender" \
smtpd_recipient_restrictions=permit_sasl_authenticated,permit_mynetworks,"reject_rbl_client",reject_unlisted_recipient,"check_policy_service inet:"
# Postfix connects to Postgrey on the interface specifically. Ensure that
# Postgrey listens on the same interface (and not IPv6, for instance).
# A lot of legit mail servers try to resend before 300 seconds.
# As a matter of fact RFC is not strict about retry timer so postfix and
# other MTA have their own intervals. To fix the problem of receiving
# e-mails really latter, delay of greylisting has been set to
# 180 seconds (default is 300 seconds).
tools/ /etc/default/postgrey \
POSTGREY_OPTS=\"'--inet= --delay=180'\"
# We are going to setup a newer whitelist for postgrey, the version included in the distribution is old
cat > /etc/cron.daily/mailinabox-postgrey-whitelist << EOF;
# Mail-in-a-Box
# check we have a postgrey_whitelist_clients file and that it is not older than 28 days
if [ ! -f /etc/postgrey/whitelist_clients ] || find /etc/postgrey/whitelist_clients -mtime +28 | grep -q '.' ; then
# ok we need to update the file, so lets try to fetch it
if curl --output /tmp/postgrey_whitelist_clients -sS --fail > /dev/null 2>&1 ; then
# if fetching hasn't failed yet then check it is a plain text file
# curl manual states that --fail sometimes still produces output
# this final check will at least check the output is not html
# before moving it into place
if [ "\$(file -b --mime-type /tmp/postgrey_whitelist_clients)" == "text/plain" ]; then
mv /tmp/postgrey_whitelist_clients /etc/postgrey/whitelist_clients
service postgrey restart
rm /tmp/postgrey_whitelist_clients
chmod +x /etc/cron.daily/mailinabox-postgrey-whitelist
# Increase the message size limit from 10MB to 128MB.
# The same limit is specified in nginx.conf for mail submitted via webmail and Z-Push.
tools/ /etc/postfix/ \
# Allow the two SMTP ports in the firewall.
ufw_allow smtp
ufw_allow smtps
ufw_allow submission
# Restart services
restart_service postfix
restart_service postgrey