How to Setup Postfix & Dovecot

13 Jan 2016

In this tutorial, we will setup a Postfix Email/SMTP server and a Dovecot IMAP server. We then configure the SSL certificate to enforce the security/privacy.

This is the communication path we will setup:

  1. Send: Your Email client -> Postfix SMTP server -> Forward to other email address.
  2. Receive: Send from other Email server -> Postfix receive the email -> Put into Dovecot directory -> you receive Email through IMAP protoco.

If you are look for a quick working example, just jump to my configuration.

Dovecot IMAP Server

Where we Store Mails?

We store the mails based on domain and user:

mail_location = maildir:/%d/%n/Maildir
mail_attribute_dict = file:/%d/%n/Maildir/dovecot-attributes

%d indicate domain, and %n indicate username. For more details, take a look at Dovecot VirtualUsers.

Configure the User and Password

Dovecot supports multiple auth methods. We use the very basic Passwd-file authenticate method.

passdb {
    args = username_format=%n /%d/passwd
    driver = passwd-file
}
userdb {
    args = username_format=%n /%d/passwd
    driver = passwd-file
}

The passwd file use the format similar to /etc/passwd. Example:

i:{PLAIN}password:1000:1000::/janzhou.org/i/:/bin/bash

Secure Dovecot

It is highly suggested to use ssl certificate to secure your IMAP transfer. Otherwise your email will show to the public:

ssl_cert = </janzhou.org/apache2/namecheap/janzhou_org.pem
ssl_key = </janzhou.org/apache2/namecheap/janzhou_org.key

In the setup process, you can temporary disable the ssl to debug the configuration:

ssl = no

Postfix Server

Use Dovecot Auth

We use dovecot auth in Postfix:

smtpd_sasl_auth_enable = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
queue_directory = /var/spool/postfix

/var/spool/postfix/private/auth is where Dovecot and Postfix communicate. To create this file, we need to config Dovecot:

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

Then restart Dovecot.

Store Email to Dovecot

We store emails to Dovecot when Postfix receives them:

mailbox_command =
mailbox_transport = lmtp:unix:private/dovecot-lmtp
mailbox_size_limit = 0
home_mailbox = Maildir/
local_recipient_maps =

We need to enable lmtp service in Dovecot:

service lmtp {
  inet_listener lmtp {
    address = 127.0.0.1
    port = 2424
  }
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
}

Secure Postfix

To secure SMTP and mail receive service:

smtpd_use_tls=yes
smtpd_tls_cert_file=/janzhou.org/apache2/namecheap/janzhou_org.pem
smtpd_tls_key_file=/janzhou.org/apache2/namecheap/janzhou_org.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

Configure Submission and SMTP

In /etc/postfix/master.cf, uncomments configurations for submission and smtps:

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_sasl_type=dovecot
  -o smtpd_sasl_security_options=noanonymous
  -o smtpd_sasl_local_domain=$myhostname
  -o smtpd_sender_login_maps=hash:/janzhou.org/mail/passwd
  -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_recipient_restrictions=
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

Quick Example

/etc/dovecot/dovecot.conf

# 2.2.13: /etc/dovecot/dovecot.conf
# OS: Linux 3.2.0-4-amd64 x86_64 Debian 8.2 ext4
auth_mechanisms = plain login
auth_verbose = yes
disable_plaintext_auth = no
log_path = /var/log/dovecot.log
mail_attribute_dict = file:/janzhou.org/mail/%n/Maildir/dovecot-attributes
mail_debug = yes
mail_location = maildir:/janzhou.org/mail/%n/Maildir
passdb {
  args = username_format=%n /janzhou.org/mail/passwd
  driver = passwd-file
}
protocols = imap lmtp
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0660
    user = postfix
  }
}
service lmtp {
  inet_listener lmtp {
    address = 127.0.0.1
    port = 2424
  }
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    group = postfix
    mode = 0600
    user = postfix
  }
}
ssl_cert = </janzhou.org/apache2/namecheap/janzhou_org.pem
ssl_key = </janzhou.org/apache2/namecheap/janzhou_org.key
userdb {
  args = username_format=%n /janzhou.org/mail/passwd
  driver = passwd-file
}
verbose_ssl = yes
protocol imap {
  imap_metadata = yes
}

/etc/postfix/main.cf

# /etc/postfix/main.cf

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

myhostname = janzhou.org
myorigin = /etc/mailname
mydestination = janzhou.org, localhost.org, , localhost
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128

relayhost =
recipient_delimiter = +
inet_interfaces = all

smtpd_sasl_auth_enable = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
queue_directory = /var/spool/postfix

mailbox_command =
mailbox_transport = lmtp:unix:private/dovecot-lmtp
mailbox_size_limit = 0
home_mailbox = Maildir/
local_recipient_maps =

smtpd_use_tls=yes
smtpd_tls_cert_file=/janzhou.org/apache2/namecheap/janzhou_org.pem
smtpd_tls_key_file=/janzhou.org/apache2/namecheap/janzhou_org.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

/etc/postfix/master.cf

#
# 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=$mua_sender_restrictions
  -o smtpd_sasl_type=dovecot
  -o smtpd_sasl_security_options=noanonymous
  -o smtpd_sasl_local_domain=$myhostname
  -o smtpd_sender_login_maps=hash:/janzhou.org/mail/passwd
  -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}