===== Setting up a Postfix + Dovecot mailserver in Debian 10 (`Buster`)=====
\\
Adapted from [[https://wiki.quietlife.nl/doku.php?id=manuals:servers:mailserver|Quietlife on Setting up a Postfix + Dovecot mailserver]].

==== Firewall ====

The following ports have to be opened in your firewall:

<code>
  25/tcp  # SMTP
  80/tcp  # HTTP (for autoconfiguration)
 587/tcp  # Submission
 993/tcp  # IMAP SSL
</code>
----
\\

==== MariaDB ====

> [[https://en.wikipedia.org/wiki/MariaDB|MariaDB]] is a community-developed fork of the [[https://en.wikipedia.org/wiki/MySQL|MySQL]] relational database management system intended to remain free under the GNU GPL.

Install the database server:

<code bash>
sudo apt install mariadb-server
</code>

Harden it:

<code bash>
sudo mysql_secure_installation
</code>

Use one file per InnoDB table:

<file bash /etc/mysql/my.cnf>
[mysqld]
innodb_file_per_table=1
</file>

Restart the daemon:

<code bash>
sudo systemctl restart mariadb.service
</code>
\\

Add a database management script:

<code python mailaccount>
#!/usr/bin/env python3

import argparse
import getpass
import subprocess

INITDB_SQL = """
CREATE DATABASE mailserver;
GRANT SELECT ON mailserver.* 
TO 'mailuser'@'localhost' IDENTIFIED BY '{mailserver_password}';

CREATE TABLE `mailserver`.`virtual_domains` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(50) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `mailserver`.`virtual_users` (
  `email` VARCHAR(100) NOT NULL,
  `domain_id` INT(11) NOT NULL,
  `password` VARCHAR(106) NOT NULL,
  PRIMARY KEY (`email`),
  FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE `mailserver`.`virtual_aliases` (
  `source` VARCHAR(100) NOT NULL,
  `domain_id` INT(11) NOT NULL,
  `destination` VARCHAR(100) NOT NULL,
  PRIMARY KEY (`source`),
  FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
"""

CHECK_DOMAIN_SQL = """
SELECT id FROM `mailserver`.`virtual_domains`
WHERE name = '{domain}'
"""

ADD_DOMAIN_SQL = """
INSERT INTO `mailserver`.`virtual_domains` (`name`)
VALUES ('{domain}');
"""

ADD_USER_SQL = """
INSERT INTO `mailserver`.`virtual_users`
  (`email`, `domain_id`, `password`)
VALUES
  ('{email}', '{domain_id}', 
  ENCRYPT('{user_password}', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))))
"""

ADD_ALIAS_SQL = """
INSERT INTO `mailserver`.`virtual_aliases`
  (`domain_id`, `source`, `destination`)
VALUES
  ('{domain_id}', '{source}', '{destination}');
"""

CHANGE_PASSWORD_SQL = """
UPDATE `mailserver`.`virtual_users`
SET password = ENCRYPT('{user_password}', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))) 
WHERE email = '{email}';
"""

def parse_arguments():
    parser = argparse.ArgumentParser()
    
    subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')
    subparsers.add_parser('initdb', help='Initialze the mailaccounts database')
    
    adduser = subparsers.add_parser('adduser', help='Add a new mail user')
    adduser.add_argument('email', metavar='EMAIL', help='The email address')
    
    changepass = subparsers.add_parser(
        'changepassword', 
        help='Change the password of a mail user')
    
    changepass.add_argument('email', metavar='EMAIL', help='The email address')
    
    subparsers.add_parser('removeuser', help='Remove a mail user')
    
    addalias = subparsers.add_parser('addalias', help='Add a new mail alias')
    addalias.add_argument('source', metavar='SOURCE', 
                          help='The source email address (alias)')
    addalias.add_argument('destination', metavar='DEST', 
                          help='The destination email address')
    
    subparsers.add_parser('removealias', help='Remove a mail user')
    
    subparsers.required = True
    return parser.parse_args()

def execute_query(query):
    output = subprocess.check_output([
            'mysql', '--execute', '%s' % query]).decode('utf-8')
    return output

def initdb():
    mailserver_password = getpass.getpass('Enter new password for the mailserver user: ')
    query = INITDB_SQL.format(mailserver_password=mailserver_password)
    execute_query(query)

def get_domain_id(domain):
    result = execute_query(CHECK_DOMAIN_SQL.format(domain=domain))
    if len(result.split()) == 2:
        return result.split()[1]

def get_and_add_domain(email):
    assert email.count('@') == 1, 'Email address is not correct!'
    domain = email.split('@')[1]
    
    domain_id = get_domain_id(domain)
    
    if not domain_id:
        execute_query(ADD_DOMAIN_SQL.format(domain=domain))
        domain_id = get_domain_id(domain) 
        print('Added domain %s' % domain)    

    return domain_id

def adduser(email):
    domain_id = get_and_add_domain(email)
    user_password = getpass.getpass('Enter new password for the mail user: ')
   
    execute_query(ADD_USER_SQL.format(email=email,
                                      domain_id=domain_id,
                                      user_password=user_password))
    
    print('Added user %s' % email)

def addalias(source, destination):
    domain_id = get_and_add_domain(source)
    execute_query(ADD_ALIAS_SQL.format(source=source,
                                       domain_id=domain_id,
                                       destination=destination))
    print('Added alias %s with destination %s' % (source, destination))

def changepass(email):
    user_password = getpass.getpass('Enter new password for the mail user: ')
    
    execute_query(CHANGE_PASSWORD_SQL.format(email=email, 
                                             user_password=user_password))
    print('Changed password of user %s' % email)

def main():
    args = parse_arguments()
    subcommand = args.subcommand
    if subcommand == 'initdb':
        initdb()
    elif subcommand == 'adduser':
        adduser(args.email)
    elif subcommand == 'addalias':
        addalias(args.source, args.destination)
    elif subcommand == 'changepassword':
        changepass(args.email)
    elif subcommand in ('removeuser','removealias'):
        raise NotImplementedError('%s is not yet implemented' % subcommand)
    
if __name__ == '__main__':
    main()
</code>

Make it executable:

<code bash>
chmod 770 ./mailaccount
</code>

Create a database called ''mailserver'' and a user called ''mailuser'':

<code bash>
sudo ./mailaccount initdb
</code>

=== Add users and aliases ===

Users:

<code bash>
sudo ./mailaccount adduser user1@quietlife.nl
</code>

Aliases:

<code bash>
sudo ./mailaccount addalias postmaster@quietlife.nl root@quietlife.nl
sudo ./mailaccount addalias root@quietlife.nl user1@quietlife.nl
</code>

----
\\

==== Postfix ====

> [[https://en.wikipedia.org/wiki/Postfix_(software)|Postfix]] is a free and open-source [[https://en.wikipedia.org/wiki/Mail_transfer_agent|mail transfer agent]] (MTA) that routes and delivers electronic mail, intended as an alternative to Sendmail MTA.

<code bash>
sudo apt install postfix postfix-mysql
</code>

\\

<file bash /etc/postfix/main.cf>
smtpd_banner = $myhostname ESMTP
biff = no
append_dot_mydomain = no
readme_directory = no
compatibility_level = 2

# TLS parameters
smtp_tls_cert_file = /etc/letsencrypt/live/quietlife.nl/fullchain.pem
smtp_tls_key_file = /etc/letsencrypt/live/quietlife.nl/privkey.pem
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/letsencrypt/live/quietlife.nl/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/quietlife.nl/privkey.pem
smtpd_tls_security_level = may
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_tls_received_header = yes

# Use strong ciphers
smtpd_tls_ciphers = high
smtpd_tls_mandatory_ciphers = high
smtpd_tls_protocols = TLSv1.2, !TLSv1.1, !TLSv1, !SSLv3, !SSLv2
smtpd_tls_mandatory_protocols = TLSv1.2, !TLSv1.1, !TLSv1, !SSLv3, !SSLv2
smtpd_tls_exclude_ciphers = MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL
smtpd_tls_mandatory_exclude_ciphers = MD5, DES, ADH, RC4, PSD, SRP, 3DES, eNULL, aNULL
smtpd_tls_eecdh_grade = ultra

tls_eecdh_ultra_curve = secp384r1
tls_high_cipherlist = AES384+EECDH:AES384+EDH:AES256+EECDH:AES256+EDH
tls_preempt_cipherlist = yes
tls_ssl_options = NO_RENEGOTIATION

# Enable SMTP for authenticated users and hand off authentication to Dovecot
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
smtpd_recipient_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_unauth_destination

# Network and host parameters
myhostname = vitas.quietlife.nl
myorigin = /etc/mailname
mydestination = localhost
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
inet_interfaces = all
inet_protocols = all

# Mail queue parameters
maximal_queue_lifetime = 12h
bounce_queue_lifetime = 12h
maximal_backoff_time = 1h
minimal_backoff_time = 5m
queue_run_delay = 5m

# Mailbox parameters
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
relayhost =
mailbox_size_limit = 51200000
message_size_limit = 51200000
recipient_delimiter = +
disable_vrfy_command = yes

# Hand off local delivery to Dovecot's LMTP and tell it where to store mail
virtual_transport = lmtp:unix:private/dovecot-lmtp

# Virtual domains, users and aliases
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf, mysql:/etc/postfix/mysql-virtual-email2email.cf

# Strip MUA headers
mime_header_checks = regexp:/etc/postfix/header_checks
header_checks = regexp:/etc/postfix/header_checks
</file>

<file bash /etc/mailname>
quietlife.nl
</file>

<file bash /etc/postfix/mysql-virtual-mailbox-domains.cf>
user = mailuser
password = example-password
hosts = 127.0.0.1
dbname = mailserver
query = SELECT 1 FROM virtual_domains WHERE name='%s'
</file>

<file bash /etc/postfix/mysql-virtual-mailbox-maps.cf>
user = mailuser
password = example-password
hosts = 127.0.0.1
dbname = mailserver
query = SELECT 1 FROM virtual_users WHERE email='%s'
</file>

<file bash /etc/postfix/mysql-virtual-alias-maps.cf>
user = mailuser
password = example-password
hosts = 127.0.0.1
dbname = mailserver
query = SELECT destination FROM virtual_aliases WHERE source='%s'
</file>

<file bash /etc/postfix/mysql-virtual-email2email.cf>
user = mailuser
password = example-password
hosts = 127.0.0.1
dbname = mailserver
query = SELECT email FROM virtual_users WHERE email='%s'
</file>

<file bash /etc/postfix/master.cf>
# ==========================================================================
# service   type  private unpriv  chroot  wakeup  maxproc command + args
#                 (yes)   (yes)   (no)    (never) (100)
# ==========================================================================
smtp        inet  n       -       y       -       -       smtpd
#smtp       inet  n       -       y       -       1       postscreen
#smtpd      pass  -       -       y       -       -       smtpd
#dnsblog    unix  -       -       y       -       0       dnsblog
#tlsproxy   unix  -       -       y       -       0       tlsproxy
submission  inet  n       -       y       -       -       smtpd
   -o syslog_name=postfix/submission
   -o smtpd_tls_security_level=encrypt
   -o smtpd_sasl_auth_enable=yes
   -o smtpd_client_restrictions=permit_sasl_authenticated,reject
   -o milter_macro_daemon_name=ORIGINATING
#  -o smtpd_reject_unlisted_recipient=no
#  -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
#smtps      inet  n       -       y       -       -       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       -       y       -       -       qmqpd
pickup      unix  n       -       y       60      1       pickup
   -o content_filter=
   -o receive_override_options=no_header_body_checks
cleanup     unix  n       -       y       -       0       cleanup
qmgr        unix  n       -       n       300     1       qmgr
#qmgr       unix  n       -       n       300     1       oqmgr
tlsmgr      unix  -       -       y       1000?   1       tlsmgr
rewrite     unix  -       -       y       -       -       trivial-rewrite
bounce      unix  -       -       y       -       0       bounce
defer       unix  -       -       y       -       0       bounce
trace       unix  -       -       y       -       0       bounce
verify      unix  -       -       y       -       1       verify
flush       unix  n       -       y       1000?   0       flush
proxymap    unix  -       -       n       -       -       proxymap
proxywrite  unix  -       -       n       -       1       proxymap
smtp        unix  -       -       y       -       -       smtp
relay       unix  -       -       y       -       -       smtp
#  -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq       unix  n       -       y       -       -       showq
error       unix  -       -       y       -       -       error
retry       unix  -       -       y       -       -       error
discard     unix  -       -       y       -       -       discard
local       unix  -       n       n       -       -       local
virtual     unix  -       n       n       -       -       virtual
lmtp        unix  -       -       y       -       -       lmtp
anvil       unix  -       -       y       -       1       anvil
scache      unix  -       -       y       -       1       scache
</file>

<file bash /etc/postfix/header_checks>
/^Received:.*with ESMTPSA/      IGNORE
/^X-Originating-IP:/            IGNORE
/^X-Mailer:/                    IGNORE
/^Mime-Version:/                IGNORE
</file>
\\

Refresh aliases:

<code bash>
sudo newaliases
sudo postmap /etc/aliases
</code>

----
\\
==== Dovecot ====

> [[https://en.wikipedia.org/wiki/Dovecot_(software)|Dovecot]] is an open-source IMAP and POP3 server for Linux/UNIX-like systems, written primarily with security in mind.

<code bash>
sudo apt install dovecot-core dovecot-imapd dovecot-lmtpd dovecot-mysql
</code>

Create a ''vmail'' user and ''vmail'' group and set permissions:

<code bash>
sudo groupadd -g 5000 vmail
sudo useradd -g vmail -u 5000 vmail -d /var/mail
sudo chown -R vmail:vmail /var/mail
sudo mkdir -p /var/mail/vhosts/quietlife.nl
sudo chmod 2700 /var/mail/vhosts/*
sudo chown -R vmail:dovecot /etc/dovecot
</code>
\\

<file bash /etc/dovecot/dovecot.conf>
# Enable installed protocols
!include_try /usr/share/dovecot/protocols.d/*.protocol
protocols = imap lmtp
</file>

<file bash /etc/dovecot/conf.d/10-mail.conf>
# Location for users' mailboxes.
mail_location = maildir:/var/mail/vhosts/%d/%n

[...]

# Group to enable temporarily for privileged operations.
mail_privileged_group = mail
</file>

<file bash /etc/dovecot/conf.d/10-auth.conf>
# Disable LOGIN command and all other plaintext authentications unless
# SSL/TLS is used (LOGINDISABLED capability).
disable_plaintext_auth = yes

[...]

# Space separated list of wanted authentication mechanisms:
auth_mechanisms = plain login

[...]

## Password and user databases
##
#!include auth-system.conf.ext
!include auth-sql.conf.ext
</file>

<file bash /etc/dovecot/conf.d/auth-sql.conf.ext>
passdb {
  driver = sql
  args = /etc/dovecot/dovecot-sql.conf.ext
}

[...]

userdb {
  driver = static
  args = uid=vmail gid=vmail home=/var/mail/vhosts/%d/%n
}
</file>

<file bash /etc/dovecot/dovecot-sql.conf.ext>
# Database driver: mysql, pgsql, sqlite
driver = mysql

[...]

# Database connection string. This is driver-specific setting.
connect = host=127.0.0.1 dbname=mailserver user=mailuser password=example_password

[...]

# Default password scheme.
default_pass_scheme = SHA512-CRYPT

[...]

# passdb query to retrieve the password.
password_query = SELECT email as user, password FROM virtual_users WHERE email='%u';
</file>

<file bash /etc/dovecot/conf.d/10-master.conf>
# Enable imaps on port 993 only (disable imap on port 143)
service imap-login {
  inet_listener imap {
    port = 0
  }
  inet_listener imaps {
    port = 993
    ssl = yes
  }

[...]

# Disable pop3s and pop3
service pop3-login {
  inet_listener pop3 {
    port = 0
  }
  inet_listener pop3s {
    port = 0
    #ssl = yes
  }
}

# Enable lmtp for local delivery
service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    mode = 0600
    user = postfix
    group = postfix
  }
}

[...]

service auth {

  unix_listener auth-userdb {
    mode = 0600
    user = vmail
    #group =
  }

  # Postfix smtp-auth
  unix_listener /var/spool/postfix/private/auth {
    mode = 0666
    user = postfix
    group = postfix
  }

  # Auth process is run as this user.
  user = dovecot
}

service auth-worker {
  user = vmail
}
</file>

<file bash /etc/dovecot/conf.d/10-ssl.conf>
# SSL/TLS support: yes, no, required.
ssl = required

[...]

# PEM encoded X.509 SSL/TLS certificate and private key.
ssl_cert = </etc/letsencrypt/live/quietlife.nl/fullchain.pem 
ssl_key = </etc/letsencrypt/live/quietlife.nl/privkey.pem

[...]

# DH parameters length to use
ssl_dh_parameters_length = 2048

# SSL protocols (not) to use
ssl_protocols = !SSLv3 !TLSv1 !TLSv1.1

# SSL ciphers to use
ssl_cipher_list = AES384+EECDH:AES384+EDH:AES256+EECDH:AES256+EDH

# Prefer the server's order of ciphers over client's
ssl_prefer_server_ciphers = yes 
</file>

----
\\
==== Sender Policy Framework ====

> [[https://en.wikipedia.org/wiki/Sender_Policy_Framework|Sender Policy Framework]] (SPF) is a simple email-validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchangers to check that incoming mail from a domain comes from a host authorized by that domain's administrators.

<code bash>
sudo apt install postfix-pcre postfix-policyd-spf-python
</code>
\\

Add SPF to the Postfix configuration:

Change

<file bash /etc/postfix/main.cf>
smtpd_recipient_restrictions = 
        permit_sasl_authenticated, 
        permit_mynetworks, 
        reject_unauth_destination
</file>

to

<file bash /etc/postfix/main.cf>
smtpd_recipient_restrictions = 
        permit_sasl_authenticated, 
        permit_mynetworks, 
        reject_unauth_destination,
        check_policy_service unix:private/policyd-spf

policyd-spf_time_limit = 3600
</file>

(Mind the comma!)

<file bash /etc/postfix/master.cf>
[...]

# SPF configuration
policyd-spf unix  -       n       n       -       0       spawn
  user=policyd-spf argv=/usr/bin/policyd-spf
</file>
\\

Finally, add a DNS TXT record for ''@'' (or ''quietlife.nl.''), containing:

<code bash>
"v=spf1 mx -all"
</code>

This tells the receiving mailserver that all mails coming from your domain should originate from the IP's in your A / AAAA records. 

----
\\

==== OpenDKIM ====

> [[https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail|DomainKeys Identified Mail]] (DKIM) is an email authentication method designed to detect email spoofing. It allows the receiver to check that an email claimed to have come from a specific domain was indeed authorized by the owner of that domain.

<code bash>
sudo apt install opendkim opendkim-tools unbound
</code>

Add the ''opendkim'' user to the ''postfix'' group:

<code bash>
sudo adduser postfix opendkim
</code>

Create an ''/etc/opendkim'' directory to store the tables:

<code bash>
sudo mkdir /etc/opendkim
</code>
\\

<file bash /etc/opendkim.conf>
# Log to syslog
Syslog                  yes

# Required to use local socket with MTAs that access the socket as a non-
# privileged user (e.g. Postfix)
UMask                   002

# Sign for example.com with key in /etc/dkimkeys/dkim.key using
# selector '2007' (e.g. 2007._domainkey.example.com)
# Domain                example.com
# KeyFile               /etc/mail/dkim.key
# Selector              2007

KeyTable                /etc/opendkim/key.table
SigningTable            refile:/etc/opendkim/signing.table
ExternalIgnoreList      /etc/opendkim/trusted.hosts
InternalHosts           /etc/opendkim/trusted.hosts

# Commonly-used options; the commented-out versions show the defaults.
Canonicalization        relaxed/simple
Mode                    sv
SubDomains              no
OversignHeaders         From

[...]

TrustAnchorFile         /usr/share/dns/root.key
</file>

Change the ''201708'' example to the current year/month:

<file bash /etc/opendkim/key.table>
quietlife       quietlife.nl:201708:/etc/dkimkeys/quietlife.private
</file>

<file bash /etc/opendkim/signing.table>
*@quietlife.nl  quietlife
</file>

Add localhost, your hostname, your domain name(s) and your FQDN to the trusted hosts:

<file bash /etc/opendkim/trusted.hosts>
127.0.0.1
::1
localhost
vitas
quietlife.nl
vitas.quietlife.nl
</file>

<file bash /etc/default/opendkim>
# Change to /var/spool/postfix/var/run/opendkim to use a Unix socket with
# postfix in a chroot:
RUNDIR=/var/spool/postfix/var/run/opendkim

[...]

# Uncomment to specify an alternate socket
SOCKET=local:$RUNDIR/opendkim.sock

[...]

USER=opendkim
GROUP=postfix
PIDFILE=$RUNDIR/$NAME.pid
</file>

Generate a systemd unit file:

<code bash>
sudo /lib/opendkim/opendkim.service.generate
sudo systemctl daemon-reload
</code>
\\

Add OpenDKIM to the Postfix configuration:

<code bash>
sudo mkdir /var/spool/postfix/var/run/opendkim
sudo chown opendkim:postfix /var/spool/postfix/var/run/opendkim
</code>

<file bash /etc/postfix/main.cf>
[...]

# Use OpenDKIM to sign and verify mail
milter_default_action = accept
milter_protocol = 6
smtpd_milters = unix:var/run/opendkim/opendkim.sock
non_smtpd_milters = unix:var/run/opendkim/opendkim.sock
</file>
\\

Generate keys (use the current year/month instead of the example ''201708''):

<code bash>
opendkim-genkey -b 2048 -h rsa-sha256 -r -s 201708 -d quietlife.nl -v
sudo mv 201708.private /etc/dkimkeys/quietlife.private
mv 201708.txt dns.txt
</code>
\\

Finally, add a DNS TXT record with the contents of ''dns.txt'':

<code bash>
201708._domainkey  3600  IN  TXT  "v=DKIM1; h=sha256; k=rsa; s=email; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA63ggTqo80JaQBGV2uNreiX2/2yQx3PHbh9/4k+gIYO71ujqjGblk5z2FgzbWrTaIU7fZ0nN09bZAVDYavc9817fpYIYvnenDdKPJazl4hiVbBJL8jZ8/0ndu5WkCIzY60ukI423IAK+ppx7UW7Tpq38RokyFW8Wq96RAuhqeGkdxQN03N//yAtRCmeWwHw+jdGGq1WGbOKE7LcigRBMW9xPdJOk/rQPU2OjRh3b/BLohMYY0NX+0+Ybp0+5JuO6NZeYqWKbvezhtltTPrsYJU1m3cJTv11UxYiI8QPmSPGMJKVUevQv6Pn2aCARuNPIxSqfGwW6iwBhUZuxb1zQPCwIDAQAB"
</code>

(Change ''h=rsa-sha256'' to ''h=sha256'' and cut the key starting with ''v=DKIM1; ...'')

----
\\
==== Amavis ====

> [[https://en.wikipedia.org/wiki/Amavis|Amavis]] is an open source content filter for electronic mail, implementing mail message transfer, decoding, some processing and checking, and interfacing with external content filters to provide protection against spam, viruses and other malware.

<code bash>
sudo apt install amavisd-new pyzor razor p7zip-full spamassassin
</code>

Set up razor:

<code bash>
sudo su - amavis -s /bin/bash
razor-admin -create
razor-admin -register
exit
</code>
\\

<file bash /etc/amavis/conf.d/15-content_filter_mode>
# Default SPAM checking mode
# Please note, that anti-spam checking is DISABLED by
# default.
# If You wish to enable it, please uncomment the following lines:
@bypass_spam_checks_maps = (
   \%bypass_spam_checks, \@bypass_spam_checks_acl, \$bypass_spam_checks_re);
</file>

<file bash /etc/amavis/conf.d/50-user>
$undecipherable_subject_tag = undef;
$virus_admin = undef;
$spam_admin = undef;
</file>

<file bash /etc/amavis/conf.d/05-node_id>
# To manually set $myhostname, edit the following line with the correct Fully
# Qualified Domain Name (FQDN) and remove the # at the beginning of the line.
$myhostname = "localhost";
</file>

Add Amavis to the Postfix configuration:

<file bash /etc/postfix/main.cf>
[...]

# Use Amavis to filter content
content_filter = smtp-amavis:[127.0.0.1]:10024
</file>

<file bash /etc/postfix/master.cf>
[...]

# Amavis configuration
smtp-amavis unix  -       -       -       -       2       smtp
   -o smtp_data_done_timeout=1200
   -o smtp_send_xforward_command=yes
   -o disable_dns_lookups=yes
   -o max_use=20
127.0.0.1:10025 inet n    -       -       -       -       smtpd
   -o content_filter=
   -o local_recipient_maps=
   -o relay_recipient_maps=
   -o smtpd_restriction_classes=
   -o smtpd_delay_reject=no
   -o smtpd_client_restrictions=permit_mynetworks,reject
   -o smtpd_helo_restrictions=
   -o smtpd_sender_restrictions=
   -o smtpd_recipient_restrictions=permit_mynetworks,reject
   -o smtpd_data_restrictions=reject_unauth_pipelining
   -o smtpd_end_of_data_restrictions=
   -o mynetworks=127.0.0.0/8
   -o smtpd_error_sleep_time=0
   -o smtpd_soft_error_limit=1001
   -o smtpd_hard_error_limit=1000
   -o smtpd_client_connection_count_limit=0
   -o smtpd_client_connection_rate_limit=0
   -o receive_override_options=no_header_body_checks,no_unknown_recipient_checks,no_milters
</file>

----
\\
==== Postgrey ====

> [[https://en.wikipedia.org/wiki/Greylisting|Greylisting]] is a method of defending email users against spam. A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate the originating server will try again after a delay, and if sufficient time has elapsed the email will be accepted.

<code bash>
sudo apt install postgrey libnet-rblclient-perl libparse-syslog-perl
</code>
\\

<file bash /etc/default/postgrey>
POSTGREY_OPTS="--inet=10023 --delay=60"
</file>

Add Postgrey to the Postfix configuration:

Change

<file bash /etc/postfix/main.cf>
smtpd_recipient_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_unauth_destination,
        check_policy_service unix:private/policyd-spf
</file>

to

<file bash /etc/postfix/main.cf>
smtpd_recipient_restrictions =
        permit_sasl_authenticated,
        permit_mynetworks,
        reject_unauth_destination,
        check_policy_service unix:private/policyd-spf,
        check_policy_service inet:127.0.0.1:10023
</file>

(Mind the comma!)

----
\\

==== Fail2ban ====

> [[https://en.wikipedia.org/wiki/Fail2ban|Fail2Ban]] is an intrusion prevention software framework that protects computer servers from brute-force attacks.

<code bash>
sudo apt install fail2ban
</code>

Copy ''jail.conf'' to ''jail.local'':

<code bash>
sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local
</code>
\\

<file bash /etc/fail2ban/jail.local>
# Mail servers

[postfix]
enabled  = true
port     = smtp,465,submission
logpath  = %(postfix_log)s
backend  = %(postfix_backend)s

[postfix-rbl]
enabled  = true
port     = smtp,465,submission
logpath  = %(postfix_log)s
backend  = %(postfix_backend)s
maxretry = 1

[...]

[dovecot]
enabled = true
port    = pop3,pop3s,imap,imaps,submission,465,sieve
logpath = %(dovecot_log)s
backend = %(dovecot_backend)s

[...]

# Mail servers authenticators: might be used for smtp,ftp,imap servers, so
# all relevant ports get banned

[postfix-auth]                                                                                                                                                                      
enabled  = true                                                                                                                                                                     
filter   = postfix-auth                                                                                                                                                             
action   = iptables-multiport[name=postfix, port="http,https,smtp,submission,pop3,pop3s,imap,imaps,sieve", protocol=tcp]                                                            
logpath  = /var/log/mail.log

[postfix-sasl]
enabled  = true
port     = smtp,465,submission,imap3,imaps,pop3,pop3s
logpath  = %(postfix_log)s
backend  = %(postfix_backend)s
</file>

By default, Fail2ban does not ship with a Postfix SMTP auth filter, so create one:

<file bash /etc/fail2ban/filter.d/postfix-auth.conf>
[Definition]
failregex = lost connection after (AUTH|UNKNOWN|EHLO) from (.*)\[<HOST>\]
ignoreregex =
</file>

----
\\

==== Client autoconfiguration ====

> The goal of [[https://developer.mozilla.org/docs/Mozilla/Thunderbird/Autoconfiguration|autoconfiguration]] is to make it very easy for users to configure the connection to their email servers.

This guide assumes you use Apache or nginx, but any HTTP server will suffice.

The result is an autoconfiguration URL that mail clients like Thunderbird can parse to preconfigure settings.

=== Apache ===

<file apache /etc/apache2/sites-available/autoconfig.quietlife.nl.conf>
<VirtualHost *:80>
   ServerName autoconfig.quietlife.nl
   DocumentRoot /var/www/autoconfig.quietlife.nl
    <Directory /var/www/autoconfig.quietlife.nl>
     Order allow,deny
     allow from all
    </Directory>
</VirtualHost>
</file>

Enable it:

<code bash>
sudo a2ensite autoconfig.quietlife.nl.conf
sudo systemctl reload apache2.service
</code>
\\

=== nginx ===

<file nginx /etc/nginx/sites-available/autoconfig.quietlife.nl>
server {
        listen 80;
        listen [::]:80;
        server_name autoconfig.quietlife.nl;
        root /var/www/autoconfig.quietlife.nl;
}
</file>

Enable it:

<code bash>
cd /etc/nginx/sites-enabled/
sudo ln -s ../sites-available/autoconfig.quietlife.nl autoconfig.quietlife.nl
sudo systemctl reload nginx.service
</code>
\\

=== Configuration ===

<file xml /var/www/autoconfig.quietlife.nl/mail/config-v1.1.xml>
<?xml version="1.0" encoding="UTF-8"?>
<clientConfig version="1.1">
 <emailProvider id="quietlife.nl">
  <domain>quietlife.nl</domain>
  <displayName>quietlife.nl</displayName>
  <displayShortName>quietlife</displayShortName>
   <incomingServer type="imap">
    <hostname>quietlife.nl</hostname>
    <port>993</port>
    <socketType>SSL</socketType>
    <authentication>password-cleartext</authentication>
    <username>%EMAILADDRESS%</username>
   </incomingServer>
   <outgoingServer type="smtp">
    <hostname>quietlife.nl</hostname>
    <port>587</port>
    <socketType>STARTTLS</socketType>
    <authentication>password-cleartext</authentication>
    <username>%EMAILADDRESS%</username>
   </outgoingServer>
 </emailProvider>
</clientConfig>
</file>

----
\\

==== Starting everything up ====

<code bash>
sudo systemctl restart postfix.service dovecot.service opendkim.service postgrey.service amavis.service fail2ban.service
</code>
----

\\

==== Testing ====

> [[https://en.wikipedia.org/wiki/Failure|Failure]] is the state or condition of not meeting a desirable or intended objective, and may be viewed as the opposite of success.

=== Test your mail server status ===

Go to [[https://mxtoolbox.com/domain/|MxToolBox]] and run a test. Ideally, you should not see any problems.\\
\\

=== Test DKIM DNS record ===

<code bash>
opendkim-testkey -d quietlife.nl -s 201708
</code>

If nothing is shown, your DNS record is set up properly.\\
\\

=== Test signatures ===

Send an empty email to [[check-auth@verifier.port25.com|port25.com's verifier]]. It should return this:

<code>
==========================================================
Summary of Results
==========================================================
SPF check:          pass
DKIM check:         pass
SpamAssassin check: ham
</code>

----
\\

==== Author Domain Signing Practices ====

> In computing, [[https://en.wikipedia.org/wiki/Author_Domain_Signing_Practices|Author Domain Signing Practices]] (ADSP) is an optional extension to the DKIM email authentication scheme, whereby a domain can publish the signing practices it adopts when relaying mail on behalf of associated authors.

If DKIM is working well, you can set up an ADSP record, telling the receiving mailserver that all mails coming from your domain should have a valid DKIM signature.

Add a DNS TXT record containing this:

<code bash>
_adsp._domainkey  3600  IN  TXT  "dkim=all"
</code>

----
\\

==== Domain-based Message Authentication, Reporting & Conformance ====

> [[https://en.wikipedia.org/wiki/DMARC|Domain-based Message Authentication, Reporting and Conformance]] (DMARC) is an email-validation system designed to detect and prevent email spoofing. It is intended to combat certain techniques often used in phishing and email spam, such as emails with forged sender addresses that appear to originate from legitimate organizations.

If SPF and DKIM are working well, you can set up a DMARC record.

Add a DNS TXT record containing this: 

<code bash>
_dmarc  3600  IN  TXT  "v=DMARC1; p=reject"
</code>
\\

If you want to receive aggregate reports, you can set a ''rua'' option:

<code bash>
_dmarc  3600  IN  TXT  "v=DMARC1; p=reject; rua=mailto:postmaster@quietlife.nl"
</code>


If you also want to receive failure reports, you can set a ''ruf'' option:

<code bash>
_dmarc  3600  IN  TXT  "v=DMARC1; p=reject; rua=mailto:postmaster@quietlife.nl; ruf=mailto:postmaster@quietlife.nl"
</code>
\\

More information about DMARC records can be found [[https://dmarc.org/wiki/FAQ|here]].

----