nov 022013
 

Deze post beschrijft de installatie van een mailserver op Ubuntu 12.04.
De volgende pakketten ga ik installeren:

  • Postfix 2.9.1
  • Dovecot 2.0.19
  • MySQL 5.5.22, with anti-spam packages in the form of
  •   amavisd-new 2.6.5,
  •   Clam AntiVirus 0.97.3,
  •   SpamAssassin 3.3.2, and
  •   Postgrey 1.3.4.
  • Munin
  • Postfix Admin 2.3.6

1) Introductie

Building a Linux mailserver from scratch to your own liking is a painful process unless you happen to be one of the few folk who do that day in and day out – there’s no way around that fact. A mailserver generally consists of a range of different packages that separately handle SMTP, POP/IMAP, local storage of mail, and spam-related tasks: they must all talk to one another correctly, all have small novels in place of configuration documentation, and there is no one obvious best practice for how users are managed, how to store user data, or how to glue the various different components together. There are any number of different viable setups for moving mail between Postfix and Dovecot, for example. Further, the whole assembly tends to be unforgiving on matters such as permissions, choice of users for specific processes, and tiny errors in esoteric configuration files. Unless you know what you are doing the end result will likely be either insecure, non-functional, or otherwise misconfigured.

There are a number of fairly up to date recipes for creating mailservers out there; one of the better ones is an Ubuntu recipe by Ivar Abrahamsen, which gives you Postfix for SMTP, Courier for IMAP/POP, MySQL to store account information, virtual user mail directories, and an array of anti-spam tools that are highly effective when working in concert. It’s a good set of documents, as the author places an emphasis on producing a secure mailserver as the end result.

There are also a great many partial recipes and out of date guides that are frankly more of a hindrance than a help – especially when it comes to Dovecot, which has changed greatly between its 1.* and 2.* versions. The configuration is completely different, and so are many of the administrative and tool binaries.

I’ve used Abrahamsen’s guide as a basis for my mail servers running on AWS for a few years now. Upgrade time always rolls around eventually, however, and this time I decided to move to a new setup to mark the release of Ubuntu 12.04: swap out Courier for Dovecot and try out a web front-end for managing mail users. Finding a good all-in-one-place guide was a challenge, however – hence this document.

2) Outlining the Goal

The end result of following this guide will be a secure mail server for your domain equipped with the following software packages:

  • Postfix: sends and receives mail via the SMTP protocol. It will only relay mail on to other mailservers if the mail is sent by an authenticated user, but anyone can send mail to this server for local delivery.
  • Dovecot: a POP and IMAP server that manages local mail directories and allows users to log in and download their mail. It also handles user authentication.
  • Postgrey: greylists incoming mail, requiring unfamiliar deliverers to wait for a while and then resend. This is one of the better tools for cutting down on spam.
  • amavisd-new: a manager for organizing various antivirus and spam checking content filters.
  • Clam AntiVirus: a virus detection suite.
  • SpamAssassin: for sniffing out spam in emails.
  • Postfix Admin: a web front end for administering mail users and domains.
  • Horde Groupware Webmail Edition: a webmail interface for users.

The server will accept plain text or encrypted SMTP and POP/IMAP connections at the standard ports, but will not allow user authentication without encryption. It will pass through a minimal set of mail headers for mail sent by local users, removing identifying information from the original sender’s mail software.

3) Fire up an Ubuntu 12.04 AWS Instance with a Suitable Security Group

Start up an Elastic Block Store (EBS) server instance – at the time of writing, Ubuntu 12.04 is one of the options right there in the quick start menu for launching a new instance. Mail servers don’t generally have to be all that big if you aren’t in the business of email; a micro instance has served me just fine for a fairly well trafficked web site with a mailing list of thousands, for example. That said, the server produced by following this guide runs at close to 80% memory utilization for a micro instance when operating unloaded – a sudden blizzard of unexpected web traffic would probably cause issues. So adjust your expectations accordingly.

Firewall settings in AWS are managed through assignment of Security Groups. You’ll probably want to create one before starting the server. The Security Group should allow inbound TCP traffic from any IP address to these ports: 25 (SMTP), 80 (HTTP), 110 (POP3), 143 (IMAP), 443 (HTTPS), 465 (SMTPS), 993 (IMAPS), and 995 (POP3S). That is in addition to whatever rules you might have for SSH access over port 22 – it is not a good idea to leave that open to the world, so lock it down to the IP address ranges you use.

In fact it is a good idea to restrict all inbound traffic to the server to your IP address ranges while you are building it. You can adjust the rules to allow traffic from the rest of the world after you’re certain that everything is secure and shipshape.

4) Some Basic Configuration

The baseline Ubuntu instance is lacking in near every package you might need, so you are building from fairly close to scratch. You’ll log in as the “ubuntu” user and then switch to root; most of what you need to do requires root access:

1
sudo su

You must set up an Elastic IP to give your server a permanent IP address. By default, an AWS instance will have its own strange-looking hostname, so changing to the domain the server will have is the first item on the list:

1
hostname mail.example.com

Now set the contents of /etc/hostname to be the hostname:

1
mail.example.com

And add your hostname to the first line of /etc/hosts:

1
2
3
4
127.0.0.1 mail.example.com localhost
# Usually some IPv6 configuration below the first line, but leave that alone.
...

Now you’ll want to regenerate the server’s default self-signed SSL certificate so that it matches the domain name. You may have purchased an SSL certificate for your mail server, but it is perfectly possible and completely secure to run a mail server using a self-signed certificate. The only consequences will be warning screens when using webmail hosted on the server and warnings from Microsoft Outlook when connecting via POP, IMAP, or SMTP.

1
2
apt-get install ssl-cert
make-ssl-cert generate-default-snakeoil --force-overwrite

5) Now Build a LAMP Web Server

You will need the mailserver to also be a LAMP (Linux, Apache, MySQL, PHP) web server, since you will want webmail and a web-based administrative interface for managing users. So turning your Ubuntu instance into a web server is a good place to start. There is a shortcut to install the basic LAMP packages, so start by updating the repository data and installing the packages. Notice the “^” at the end of the command there – it is necessary:

1
2
3
apt-get update
apt-get upgrade
apt-get install lamp-server^

During this install you will be asked to choose a root password for MySQL. Choose something sensible, and then move on to adding an array of basic additional packages for PHP – such as APC bytecode caching, memcache support, cURL, an XML parser, and GD image processing. Add more to suite your own taste and the applications you want to support on this server.

1
apt-get install php-apc php5-memcache php5-curl php5-gd php-xml-parser

6) Configure PHP

The default configuration for PHP and the additional packages mentioned above is sufficient for most casual usage. So unless you have something complicated or high-powered in mind, you should probably only change the expose_php setting in /etc/php5/apache2/php.ini. Set it to “Off”:

1
2
3
4
5
6
; Decides whether PHP may expose the fact that it is installed on the server
; (e.g. by adding its signature to the Web server header).  It is no security
; threat in any way, but it makes it possible to determine whether you use PHP
; on your server or not.
expose_php = Off

7) Configure Apache

The expected end result for Apache is that it will serve a single site with a couple of running web applications: webmail and Postfix Admin hidden away in a subdirectory. All traffic will be directed to HTTPS – there is no good reason to allow non-secure access to any of what will be on the web server.

Firstly configure the following lines in /etc/apache2/conf.d/security to minimize the information that Apache gives out in its response headers:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
#
# ServerTokens
# This directive configures what you return as the Server HTTP response
# Header. The default is 'Full' which sends information about the OS-Type
# and compiled in modules.
# Set to one of:  Full | OS | Minimal | Minor | Major | Prod
# where Full conveys the most information, and Prod the least.
#
ServerTokens Prod
#
# Optionally add a line containing the server version and virtual host
# name to server-generated pages (internal error documents, FTP directory
# listings, mod_status and mod_info output etc., but not CGI generated
# documents or custom error documents).
# Set to "EMail" to also include a mailto: link to the ServerAdmin.
# Set to one of:  On | Off | EMail
#
ServerSignature Off

Make sure that mod_rewritemod_ssl, and the default SSL virtual host is enabled – you’ll need these line items to be able to force visitors to use HTTPS.

1
2
a2enmod rewrite ssl
a2ensite default-ssl

The default site configuration in /etc/apache2/sites-available/default can be edited to look something like this for the sake of simplicity:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
<VirtualHost *:80>
  ServerAdmin webmaster@localhost
  DocumentRoot /var/www
  <Directory "/">
    Options FollowSymLinks
    AllowOverride All
  </Directory>
  ErrorLog ${APACHE_LOG_DIR}/error.log
  # Possible values include: debug, info, notice, warn, error, crit,
  # alert, emerg.
  LogLevel warn
  CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

But of course your taste and needs may vary. Keeping the same simple approach, the upper portion of the SSL configuration in /etc/apache2/sites-available/default-ssl can be set up as follows:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
<IfModule mod_ssl.c>
  <VirtualHost _default_:443>
    ServerAdmin webmaster@localhost
    DocumentRoot /var/www
    <Directory "/">
      Options FollowSymLinks
      AllowOverride All
    </Directory>
    ErrorLog ${APACHE_LOG_DIR}/error.log
    # Possible values include: debug, info, notice, warn, error, crit,
    # alert, emerg.
    LogLevel warn
    CustomLog ${APACHE_LOG_DIR}/ssl_access.log combined
    #   SSL Engine Switch:
    #   Enable/Disable SSL for this virtual host.
    SSLEngine on
    #
    # ... more default SSL configuration ...
    # You will probably need to change this next Directory directive as well
    # in order to match the earlier one.
    <Directory "/">
      SSLOptions +StdEnvVars
    </Directory>
    # ... yet more default SSL configuration ...

If you are using a purchased rather than self-signed SSL certificate, and you probably have a CA certificate bundle from the issuer, then you’ll want to further change these lines in /etc/apache2/sites-enabled/default-ssl:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
#   A self-signed (snakeoil) certificate can be created by installing
#   the ssl-cert package. See
#   /usr/share/doc/apache2.2-common/README.Debian.gz for more info.
#   If both key and certificate are stored in the same file, only the
#   SSLCertificateFile directive is needed.
SSLCertificateFile    /path/to/my/cert.crt
SSLCertificateKeyFile /path/to/my/key.key
#   Server Certificate Chain:
#   Point SSLCertificateChainFile at a file containing the
#   concatenation of PEM encoded CA certificates which form the
#   certificate chain for the server certificate. Alternatively
#   the referenced file can be the same as SSLCertificateFile
#   when the CA certificates are directly appended to the server
#   certificate for convinience.
SSLCertificateChainFile /path/to/my/ca-bundle.crt

To push visitors to HTTPS, put something similar to the following snippet into /var/www/.htaccess:

1
2
3
RewriteEngine On
RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*) https://mail.example.com/$1 [L]

8) Install and Configure Memcached

You will need to install Memcached to support the webmail applications intended to run on this server:

1
apt-get install memcached

The default configuration file at /etc/memcached.conf is good enough for a small server: it locks down access to localhost and provides generally sensible configuration parameter values. If you are building a larger machine for heavy usage, you will probably want to bump the memory allocation to be higher than the default of 64M:

1
2
3
4
# Start with a cap of 64 megs of memory. It's reasonable, and the daemon default
# Note that the daemon will grow to this size, but does not start out holding this much
# memory
-m 64

9) Install the Mailserver Packages

Now we’re ready to start in on the harder stuff. As for the LAMP server, there is a shortcut for installing the basic packages for a mail server. Again, note the “^” at the end of the command:

1
apt-get install mail-server^

When Postfix installs, you will be asked to choose a general type of mail configuration – select “Internet site”. You will be asked for the system mail name, which is the hostname of your mailserver – e.g. mail.example.com. What this gives you is pretty much just bare bones, aimed at a mailserver that manages its users as straightforward Unix users, and which doesn’t use a SQL database to store data. So we need the rest of the cast – such as MySQL support for Postfix and Dovecot, and the coterie of spam-mashing packages. You might also have to install IMAP support for Dovecot, as it may or may not be included in the mail-server packages:

1
2
3
apt-get install postfix-mysql dovecot-mysql dovecot-imapd postgrey
apt-get install amavis clamav clamav-daemon spamassassin
apt-get install php5-imap

The php5-imap package actually supports POP3 as well as the IMAP protocol, and will be needed by Postfix Admin and many of the possible options for PHP webmail applications. Restart Apache to have that running and ready:

1
service apache2 restart

Next you’ll want some optional packages that extend the abilities of the spam and virus detection packages, such as by allowing greater inspection of attached files:

1
2
apt-get install libnet-dns-perl pyzor razor
apt-get install arj bzip2 cabextract cpio file gzip nomarch pax unzip zip

You probably also want a package for dealing with RAR-format archives – but I’ve found unrar-free to be somewhat buggy and unstable, while unrar is not free. So you may just choose to skip that and shrug.

10) Create a Mail Database and User in MySQL

Log in to MySQL as the root user, entering the password you set earlier:

1
mysql -uroot -p

Now set up a database and user for the mail software. This database will store information on user accounts and mail domains, using schema set up by the Postfix Admin package:

1
2
create database mail;
grant all on mail.* to 'mail'@'localhost' identified by 'mailpassword';

11) Install Postfix Admin and the MySQL Schema

Postfix Admin is installed as follows. To start things off, download the package from Sourceforge, unpack it, and move it into a subdirectory of your webroot. You will probably also need to change ownership to the www-data user:

1
2
3
4
5
wget http://downloads.sourceforge.net/project/postfixadmin/postfixadmin/postfixadmin-2.3.6/postfixadmin-2.3.6.tar.gz
gunzip postfixadmin-2.3.6.tar.gz
tar -xf postfixadmin-2.3.6.tar
mv postfixadmin-2.3.6 /var/www/postfixadmin
chown -R www-data:www-data /var/www/postfixadmin

Next is an interesting sort of a two-phase setup process. Firstly alter the following lines in/var/www/postfixadmin/config.inc.php:

1
2
3
4
5
6
7
8
/*****************************************************************
 *  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 * You have to set $CONF['configured'] = true; before the
 * application will run!
 * Doing this implies you have changed this file as required.
 * i.e. configuring database etc; specifying setup.php password etc.
 */
$CONF['configured'] = true;
1
2
3
4
// Postfix Admin Path
// Set the location of your Postfix Admin installation here.
// YOU MUST ENTER THE COMPLETE URL e.g. http://domain.tld/postfixadmin
$CONF['postfix_admin_url'] = 'https://mail.example.com/postfixadmin';
1
2
3
4
5
6
7
8
9
// Database Config
// mysql = MySQL 3.23 and 4.0, 4.1 or 5
// mysqli = MySQL 4.1+
// pgsql = PostgreSQL
$CONF['database_type'] = 'mysql';
$CONF['database_host'] = 'localhost';
$CONF['database_user'] = 'mail';
$CONF['database_password'] = 'mailpassword';
$CONF['database_name'] = 'mail';
1
2
3
4
5
6
7
8
9
10
11
12
// Site Admin
// Define the Site Admins email address below.
// This will be used to send emails from to create mailboxes.
$CONF['admin_email'] = 'me@example.com';
// Mail Server
// Hostname (FQDN) of your mail server.
// This is used to send email to Postfix in order to create mailboxes.
//
// Set this to localhost for now, but change it later.
$CONF['smtp_server'] = 'localhost';
$CONF['smtp_port'] = '25';
1
2
3
4
5
6
7
8
9
10
// Encrypt
// In what way do you want the passwords to be crypted?
// md5crypt = internal postfix admin md5
// md5 = md5 sum of the password
// system = whatever you have set as your PHP system default
// cleartext = clear text passwords (ouch!)
// mysql_encrypt = useful for PAM integration
// authlib = support for courier-authlib style passwords
// dovecot:CRYPT-METHOD = use dovecotpw -s 'CRYPT-METHOD'. Example: dovecot:CRAM-MD5
$CONF['encrypt'] = 'md5crypt';
1
2
3
4
5
6
7
8
9
10
11
12
// Mailboxes
// If you want to store the mailboxes per domain set this to 'YES'.
// Examples:
//   YES: /usr/local/virtual/domain.tld/username@domain.tld
//   NO:  /usr/local/virtual/username@domain.tld
$CONF['domain_path'] = 'NO';
// If you don't want to have the domain in your mailbox set this to 'NO'.
// Examples:
//   YES: /usr/local/virtual/domain.tld/username@domain.tld
//   NO:  /usr/local/virtual/domain.tld/username
// Note: If $CONF['domain_path'] is set to NO, this setting will be forced to YES.
$CONF['domain_in_mailbox'] = 'YES';

Note that the last items above are only for the purposes of defining how Postfix Admin stores its data – they don’t set system paths for mailboxes. The actual system paths to virtual mailbox directories are defined in the Dovecot configuration outlined in a later section of this post.

Next open up a web browser and visit your mail server at:

Follow the instructions on that page to choose a setup password, and generate a hash of that password. Add that hash to the configuration file and save it:

1
2
3
4
// In order to setup Postfixadmin, you MUST specify a hashed password here.
// To create the hash, visit setup.php in a browser and type a password into the field,
// on submission it will be echoed out to you as a hashed value.
$CONF['setup_password'] = '...a long hash string...';

Then return to the setup page. You can now use the password you selected in order to create an initial administrator account. Postfix Admin will also automatically create its database schema at this point.

It is probably wise to restrict access to /var/www/postfixadmin/setup.php after having used it. Create a file/var/www/postfixadmin/.htaccess and put the following instructions into it:

1
2
3
<Files "setup.php">
deny from all
</Files>

12) Create the Domain and Accounts in Postfix Admin

Now navigate to the main Postfix Admin login page:

Log in as the newly created administrator account, and then choose the “New domain” option under “Domain List” in order to create the example.com domain. You can then add mail users (“Add mailbox”) and aliases (“Add alias”) while viewing your domain. This will populate the schema, but it won’t do anything else yet as none of the other mailserver components are configured to look at the database at this point.

Postfix Admin does have another useful function during this long setup process – it allows you to send mail to local users through the web interface, which is helpful when testing your configuration and chasing down errors.

13) Create a User to Handle Virtual Mail Directories

Virtual mail users are those that do not exist as Unix system users. They thus don’t use the standard Unix methods of authentication or mail delivery and don’t have home directories. That is how we are managing things here: mail users are defined in the database created by Postfix Admin rather than existing as system users. Mail will be kept in subfolders per domain and account under /var/vmail – e.g. me@example.com will have a mail directory of/var/vmail/example.com/me. All of these mail directories will be owned by a single user called vmail, and Dovecot will use the vmail user in order to create and update mail files.

1
2
3
4
useradd -r -u 150 -g mail -d /var/vmail -s /sbin/nologin -c "Virtual maildir handler" vmail
mkdir /var/vmail
chmod 770 /var/vmail
chown vmail:mail /var/vmail

Note that the user and virtual mail directory folder are using the “mail” group, and allowing other users in that group to modify the contents.

14) Configure Dovecot

Dovecot will manage IMAP and POP3 connections, local mail directories, and receive incoming mail handed off from Postfix. It will also manage authentication for SMTP connections – no point in having two separate authentication systems when Dovecot can handle both cases. Configuration is spread across a number of files in /etc/dovecotand subfolders thereof, and might seem a little intimidating, but it’s all laid out fairly logically. The first thing to do is to ensure that Dovecot is looking for user data in the database created by Postfix Admin, so edit or create the file/etc/dovecot/conf.d/auth-sql.conf.ext to have the following contents:

1
2
3
4
5
6
7
8
9
10
11
12
# Look up user passwords from a SQL database as
# defined in /etc/dovecot/dovecot-sql.conf.ext
passdb {
  driver = sql
  args = /etc/dovecot/dovecot-sql.conf.ext
}
# Look up user information from a SQL database as
# defined in /etc/dovecot/dovecot-sql.conf.ext
userdb {
  driver = sql
  args = /etc/dovecot/dovecot-sql.conf.ext
}

Now edit these lines in /etc/dovecot/dovecot-sql.conf.ext such that it uses the MySQL database created by Postfix Admin:

1
2
# Database driver: mysql, pgsql, sqlite
driver = mysql
1
2
3
4
5
6
# Examples:
#   connect = host=192.168.1.1 dbname=users
#   connect = host=sql.example.com dbname=virtual user=virtual password=blarg
#   connect = /etc/dovecot/authdb.sqlite
#
connect = host=localhost dbname=mail user=mail password=mailpassword
1
2
3
4
5
6
# Default password scheme.
#
# List of supported schemes is in
#
default_pass_scheme = MD5-CRYPT
1
2
3
4
5
# Define the query to obtain a user password.
password_query = \
  SELECT username as user, password, '/var/vmail/%d/%n' as userdb_home, \
  'maildir:/var/vmail/%d/%n' as userdb_mail, 150 as userdb_uid, 8 as userdb_gid \
  FROM mailbox WHERE username = '%u' AND active = '1'
1
2
3
4
5
# Define the query to obtain user information.
user_query = \
  SELECT '/var/vmail/%d/%n' as home, 'maildir:/var/vmail/%d/%n' as mail, \
  150 AS uid, 8 AS gid, concat('dirsize:storage=', quota) AS quota \
  FROM mailbox WHERE username = '%u' AND active = '1'

Then change the controlling definitions in /etc/dovecot/conf.d/10-auth.conf such that Dovecot will read the SQL configuration files. While you are there, you should also make sure that plaintext authentication is disabled unless the connection is encrypted or local:

1
2
3
4
5
# Disable LOGIN command and all other plaintext authentications unless
# SSL/TLS is used (LOGINDISABLED capability). Note that if the remote IP
# matches the local IP (ie. you're connecting from the same computer), the
# connection is considered secure and plaintext authentication is allowed.
disable_plaintext_auth = yes
1
2
3
4
5
# Space separated list of wanted authentication mechanisms:
#   plain login digest-md5 cram-md5 ntlm rpa apop anonymous gssapi otp skey
#   gss-spnego
# NOTE: See also disable_plaintext_auth setting.
auth_mechanisms = plain login
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
##
## Password and user databases
##
#
# Password database is used to verify user's password (and nothing more).
# You can have multiple passdbs and userdbs. This is useful if you want to
# allow both system users (/etc/passwd) and virtual users to login without
# duplicating the system users into virtual database.
#
# <doc/wiki/PasswordDatabase.txt>
#
# User database specifies where mails are located and what user/group IDs
# own them. For single-UID configuration use "static" userdb.
#
# <doc/wiki/UserDatabase.txt>
#!include auth-deny.conf.ext
#!include auth-master.conf.ext
#!include auth-system.conf.ext
# Use the SQL database configuration rather than any of these others.
!include auth-sql.conf.ext
#!include auth-ldap.conf.ext
#!include auth-passwdfile.conf.ext
#!include auth-checkpassword.conf.ext
#!include auth-vpopmail.conf.ext
#!include auth-static.conf.ext

Next up, tell Dovecot where to put the virtual user mail directories. That requires the following changes in/etc/dovecot/conf.d/10-mail.conf:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
# Location for users' mailboxes. The default is empty, which means that Dovecot
# tries to find the mailboxes automatically. This won't work if the user
# doesn't yet have any mail, so you should explicitly tell Dovecot the full
# location.
#
# If you're using mbox, giving a path to the INBOX file (eg. /var/mail/%u)
# isn't enough. You'll also need to tell Dovecot where the other mailboxes are
# kept. This is called the "root mail directory", and it must be the first
# path given in the mail_location setting.
#
# There are a few special variables you can use, eg.:
#
#   %u - username
#   %n - user part in user@domain, same as %u if there's no domain
#   %d - domain part in user@domain, empty if there's no domain
#   %h - home directory
#
# See doc/wiki/Variables.txt for full list. Some examples:
#
#   mail_location = maildir:~/Maildir
#   mail_location = mbox:~/mail:INBOX=/var/mail/%u
#   mail_location = mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%n
#
# <doc/wiki/MailLocation.txt>
#
mail_location = maildir:/var/vmail/%d/%n
1
2
3
4
5
# System user and group used to access mails. If you use multiple, userdb
# can override these by returning uid or gid fields. You can use either numbers
# or names. <doc/wiki/UserIds.txt>
mail_uid = vmail
mail_gid = mail
1
2
3
4
5
6
7
8
# Valid UID range for users, defaults to 500 and above. This is mostly
# to make sure that users can't log in as daemons or other system users.
# Note that denying root logins is hardcoded to dovecot binary and can't
# be done even if first_valid_uid is set to 0.
#
# Use the vmail user uid here.
first_valid_uid = 150
last_valid_uid = 150

If you are bringing your own SSL certificate to the party, you have to let Dovecot know about by editing these lines in /etc/dovecot/conf.d/10-ssl.conf. Remember to include your CA certificate bundle if provided with one by the certificate issuer:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
# SSL/TLS support: yes, no, required. <doc/wiki/SSL.txt>
ssl = yes
# PEM encoded X.509 SSL/TLS certificate and private key. They're opened before
# dropping root privileges, so keep the key file unreadable by anyone but
# root. Included doc/mkcert.sh can be used to easily generate self-signed
# certificate, just make sure to update the domains in dovecot-openssl.cnf
ssl_cert = </path/to/my/cert.pem
ssl_key = </path/to/my/key.pem
# If key file is password protected, give the password here. Alternatively
# give it when starting dovecot with -p parameter. Since this file is often
# world-readable, you may want to place this setting instead to a different
# root owned 0600 file by using ssl_key_password = <path.
#ssl_key_password =
# PEM encoded trusted certificate authority. Set this only if you intend to use
# ssl_verify_client_cert=yes. The file should contain the CA certificate(s)
# followed by the matching CRL(s). (e.g. ssl_ca = </etc/ssl/certs/ca.pem)
#ssl_ca = </path/to/ca.pem

Next, edit these lines in /etc/dovecot/conf.d/10-master.conf to add the Postfix option:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
service auth {
  # auth_socket_path points to this userdb socket by default. It's typically
  # used by dovecot-lda, doveadm, possibly imap process, etc. Its default
  # permissions make it readable only by root, but you may need to relax these
  # permissions. Users that have access to this socket are able to get a list
  # of all usernames and get results of everyone's userdb lookups.
  unix_listener auth-userdb {
   mode = 0600
    user = vmail
    group = mail
  }
  unix_listener /var/spool/postfix/private/auth {
    mode = 0660
    # Assuming the default Postfix user and group
    user = postfix
    group = postfix       
  }

You may have to explicitly set a postmaster address in /etc/dovecot/conf.d/15-lda.conf; if you see “Invalid settings: postmaster_address setting not given” showing up in the mail log, then this is the fix for that. Make sure that a suitable alias or mailbox exists for your chosen postmaster address:

1
2
3
# Address to use when sending rejection mails.
# Default is postmaster@<your domain>.
postmaster_address = postmaster@example.com

You’ll want to change the Dovecot configuration to be accessible to both dovecot and vmail users:

1
2
chown -R vmail:dovecot /etc/dovecot
chmod -R o-rwx /etc/dovecot

A final note on Dovecot: it only creates a user’s mail directory when mail is first delivered to that virtual user. So creating a user in Postfix Admin will not result in the immediate creation of a mail directory under /var/vmail, and that’s just fine.

15) Configure Amavis, ClamAV, and SpamAssassin

Before configuring Postfix, we may as well take a short detour into configuring the spam and virus tools. Their default configuration is close to what most people will need, and tools like SpamAssassin auto-detect many of the optional additional packages you may have installed. If you have specialist needs or greater knowledge, you can of course spend a fair amount of time here crafting intricate rules. For the casual user, this is a quick and straightforward process, however. Note that here we are putting off the portions relating to integration with Postfix – e.g. additions to the master.cf file – into the Postfix section of this post.

First add Amavis and ClamAV users to one another’s groups to enable them to collaborate:

1
2
adduser clamav amavis
adduser amavis clamav

Then turn on Amavis by editing /etc/amavis/conf.d/15-content_filter_mode – the software is disabled by default, so uncomment the @bypass… lines:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
use strict;
# You can modify this file to re-enable SPAM checking through spamassassin
# and to re-enable antivirus checking.
#
# Default antivirus checking mode
# Please note, that anti-virus checking is DISABLED by
# default.
# If You wish to enable it, please uncomment the following lines:
@bypass_virus_checks_maps = (
   \%bypass_virus_checks, \@bypass_virus_checks_acl, \$bypass_virus_checks_re);
#
# 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);
1;  # ensure a defined return

Now enable SpamAssassin by editing these lines in /etc/default/spamassassin:

1
2
# Change to one to enable spamd
ENABLED=1
1
2
3
4
# Cronjob
# Set to anything but 0 to enable the cron job to automatically update
# spamassassin's rules on a nightly basis
CRON=1

SpamAssassin under Amavis will only check mail that’s determined to be arriving for local delivery. There are a couple of ways to tell Amavis which mails are for local delivery, but here we’ll set it up to check the database set up by Postfix Admin. Edit /etc/amavis/conf.d/50-user to look like this:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
use strict;
 
#
# Place your configuration directives here.  They will override those in
# earlier files.
#
# See /usr/share/doc/amavisd-new/ for documentation and examples of
# the directives you can use in this file
#
# Three concurrent processes. This should fit into the RAM available on an
# AWS micro instance. This has to match the number of processes specified
# for Amavis in /etc/postfix/master.cf.
$max_servers  = 3;
 
# Add spam info headers if at or above that level - this ensures they
# are always added.
$sa_tag_level_deflt  = -9999;
# Check the database to see if mail is for local delivery, and thus
# should be spam checked.
@lookup_sql_dsn = (
    ['DBI:mysql:database=mail;host=127.0.0.1;port=3306',
     'mail',
     'mailpassword']);
$sql_select_policy = 'SELECT domain from domain WHERE CONCAT("@",domain) IN (%k)';
# Uncomment to bump up the log level when testing.
# $log_level = 2;
#------------ Do not modify anything below this line -------------
1;  # ensure a defined return

You will have to restart these processes to pick up the new configuration:

1
2
service amavis restart
service spamassassin restart

16) Configure Postfix

Postfix handles incoming mail via the SMTP protocol, and its configuration files have be set up to allow it to integrate with the various other packages we have installed so far. At a high level, we want Postfix to hand off incoming mail to the spam and virus checkers before passing it on to Dovecot for delivery, and to authenticate virtual users who are connecting over SMTP in order to to send mail.

Firstly create files describing for Postfix where to find information on users and domains. Note that the “hosts” directive in these files must be exactly the same as the “bind-address” in /etc/mysql/my.cnf. If one side says “localhost” and the other side says “127.0.0.1” then you may find that Postfix cannot connect to MySQL – strange but true. Here are the needed Postfix files:

/etc/postfix/mysql_virtual_alias_domainaliases_maps.cf

1
2
3
4
5
6
7
8
user = mail
password = mailpassword
hosts = 127.0.0.1
dbname = mail
query = SELECT goto FROM alias,alias_domain
  WHERE alias_domain.alias_domain = '%d'
  AND alias.address=concat('%u', '@', alias_domain.target_domain)
  AND alias.active = 1

/etc/postfix/mysql_virtual_alias_maps.cf

1
2
3
4
5
6
7
8
user = mail
password = mailpassword
hosts = 127.0.0.1
dbname = mail
table = alias
select_field = goto
where_field = address
additional_conditions = and active = '1'

/etc/postfix/mysql_virtual_domains_maps.cf

1
2
3
4
5
6
7
8
user = mail
password = mailpassword
hosts = 127.0.0.1
dbname = mail
table = domain
select_field = domain
where_field = domain
additional_conditions = and backupmx = '0' and active = '1'

/etc/postfix/mysql_virtual_mailbox_domainaliases_maps.cf

1
2
3
4
5
6
7
8
user = mail
password = mailpassword
hosts = 127.0.0.1
dbname = mail
query = SELECT maildir FROM mailbox, alias_domain
  WHERE alias_domain.alias_domain = '%d'
  AND mailbox.username=concat('%u', '@', alias_domain.target_domain )
  AND mailbox.active = 1

/etc/postfix/mysql_virtual_mailbox_maps.cf

1
2
3
4
5
6
7
8
user = mail
password = mailpassword
hosts = 127.0.0.1
dbname = mail
table = mailbox
select_field = CONCAT(domain, '/', local_part)
where_field = username
additional_conditions = and active = '1'

Now create the file /etc/postfix/header_checks, which will contain some directives to remove certain headers when relaying mail. This improves privacy for the sending users by such things as stripping the original IP address and mail software identifiers, for example. This file will be referenced in the main Postfix configuration:

1
2
3
4
5
6
/^Received:/                 IGNORE
/^User-Agent:/               IGNORE
/^X-Mailer:/                 IGNORE
/^X-Originating-IP:/         IGNORE
/^x-cr-[a-z]*:/              IGNORE
/^Thread-Index:/             IGNORE

The following is the complete main Postfix configuration file at /etc/postfix/main.cf, which contains a fair number of complex choices and options on how mail is relayed and how SMTP behaves. It is far beyond the scope of this post to explain each and every choice of best practice or configuration parameter in detail. I strongly suggest that you spend some time reading up on Postfix configuration, as this is where it is easy to fall down and produce a suboptimal or faulty mailserver.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
# See /usr/share/postfix/main.cf.dist for a commented, more complete version
# The first text sent to a connecting process.
smtpd_banner = $myhostname ESMTP $mail_name
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
readme_directory = no
# SASL parameters
# ---------------------------------
# Use Dovecot to authenticate.
smtpd_sasl_type = dovecot
# Referring to /var/spool/postfix/private/auth
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
broken_sasl_auth_clients = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_local_domain =
smtpd_sasl_authenticated_header = yes
# TLS parameters
# ---------------------------------
# Replace this with your SSL certificate path if you are using one.
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
# The snakeoil self-signed certificate has no need for a CA file. But
# if you are using your own SSL certificate, then you probably have
# a CA certificate bundle from your provider. The path to that goes
# here.
#smtpd_tls_CAfile=/path/to/ca/file
smtp_tls_note_starttls_offer = yes
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom
#smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
#smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
# Note that forcing use of TLS is going to cause breakage - most mail servers
# don't offer it and so delivery will fail, both incoming and outgoing. This is
# unfortunate given what various governmental agencies are up to these days.
# These are Postfix 2.2 only.
#
# Enable (but don't force) use of TLS on incoming smtp connections.
smtpd_use_tls = yes
smtpd_enforce_tls = no
# Enable (but don't force) use of TLS on outgoing smtp connections.
smtp_use_tls = yes
smtp_enforce_tls = no
# These are Postfix 2.3 and later.
#
# Enable (but don't force) all incoming smtp connections to use TLS.
smtpd_tls_security_level = may
# Enable (but don't force) all outgoing smtp connections to use TLS.
smtp_tls_security_level = may
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
# SMTPD parameters
# ---------------------------------
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
# will it be a permanent error or temporary
unknown_local_recipient_reject_code = 450
# how long to keep message on queue before return as failed.
# some have 3 days, I have 16 days as I am backup server for some people
# whom go on holiday with their server switched off.
maximal_queue_lifetime = 7d
# max and min time in seconds between retries if connection failed
minimal_backoff_time = 1000s
maximal_backoff_time = 8000s
# how long to wait when servers connect before receiving rest of data
smtp_helo_timeout = 60s
# how many address can be used in one message.
# effective stopper to mass spammers, accidental copy in whole address list
# but may restrict intentional mail shots.
smtpd_recipient_limit = 16
# how many error before back off.
smtpd_soft_error_limit = 3
# how many max errors before blocking it.
smtpd_hard_error_limit = 12
# This next set are important for determining who can send mail and relay mail
# to other servers. It is very important to get this right - accidentally producing
# an open relay that allows unauthenticated sending of mail is a Very Bad Thing.
#
# You are encouraged to read up on what exactly each of these options accomplish.
# Requirements for the HELO statement
smtpd_helo_restrictions = permit_mynetworks, warn_if_reject reject_non_fqdn_hostname, reject_invalid_hostname, permit
# Requirements for the sender details
smtpd_sender_restrictions = permit_sasl_authenticated, permit_mynetworks, warn_if_reject reject_non_fqdn_sender, reject_unknown_sender_domain, reject_unauth_pipelining, permit
# Requirements for the connecting server
smtpd_client_restrictions = reject_rbl_client sbl.spamhaus.org, reject_rbl_client blackholes.easynet.nl, reject_rbl_client dnsbl.njabl.org
# Requirement for the recipient address. Note that the entry for
# "check_policy_service inet:127.0.0.1:10023" enables Postgrey.
smtpd_recipient_restrictions = reject_unauth_pipelining, permit_mynetworks, permit_sasl_authenticated, reject_non_fqdn_recipient, reject_unknown_recipient_domain, reject_unauth_destination, check_policy_service inet:127.0.0.1:10023, permit
smtpd_data_restrictions = reject_unauth_pipelining
# require proper helo at connections
smtpd_helo_required = yes
# waste spammers time before rejecting them
smtpd_delay_reject = yes
disable_vrfy_command = yes
# General host and delivery info
# ----------------------------------
myhostname = mail.example.com
myorigin = /etc/hostname
# Some people see issues when setting mydestination explicitly to the server
# subdomain, while leaving it empty generally doesn't hurt. So it is left empty here.
# mydestination = mail.example.com, localhost
mydestination =
# If you have a separate web server that sends outgoing mail through this
# mailserver, you may want to add its IP address to the space-delimited list in
# mynetworks, e.g. as 111.222.333.444/32.
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
mynetworks_style = host
# This specifies where the virtual mailbox folders will be located.
virtual_mailbox_base = /var/vmail
# This is for the mailbox location for each user. The domainaliases
# map allows us to make use of Postfix Admin's domain alias feature.
virtual_mailbox_maps = mysql:/etc/postfix/mysql_virtual_mailbox_maps.cf, mysql:/etc/postfix/mysql_virtual_mailbox_domainaliases_maps.cf
# and their user id
virtual_uid_maps = static:150
# and group id
virtual_gid_maps = static:8
# This is for aliases. The domainaliases map allows us to make
# use of Postfix Admin's domain alias feature.
virtual_alias_maps = mysql:/etc/postfix/mysql_virtual_alias_maps.cf, mysql:/etc/postfix/mysql_virtual_alias_domainaliases_maps.cf
# This is for domain lookups.
virtual_mailbox_domains = mysql:/etc/postfix/mysql_virtual_domains_maps.cf
# Integration with other packages
# ---------------------------------------
# Tell postfix to hand off mail to the definition for dovecot in master.cf
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1
# Use amavis for virus and spam scanning
content_filter = amavis:[127.0.0.1]:10024
# Header manipulation
# --------------------------------------
# Getting rid of unwanted headers. See: https://posluns.com/guides/header-removal/
header_checks = regexp:/etc/postfix/header_checks
# getting rid of x-original-to
enable_original_recipient = no

To be clear, if you are using a purchased SSL certificate – and have a CA certificate bundle from the issuer – then you will have to alter these lines in /etc/postfix/main.cf:

1
2
3
4
5
6
7
8
# Replace this with your SSL certificate path if you are using one.
smtpd_tls_cert_file=/path/to/my/cert.pem
smtpd_tls_key_file=/path/to/my/key.key
# The snakeoil self-signed certificate has no need for a CA file. But
# if you are using your own SSL certificate, then you probably have
# a CA certificate bundle from your provider. The path to that goes
# here.
#smtpd_tls_CAfile=/path/to/ca/file

Further, if you are running Postfix version 2.10 or later, which might be the case if you are reading this recipe for pointers on an installation on a later version of Ubuntu, then you will need to add the following lines:

1
2
3
# This is a new option as of Postfix 2.10, and is required in addition to
# smtpd_recipient_restrictions for things to work properly in this setup.
smtpd_relay_restrictions = reject_unauth_pipelining, permit_mynetworks, permit_sasl_authenticated, reject_non_fqdn_recipient, reject_unknown_recipient_domain, reject_unauth_destination, check_policy_service inet:127.0.0.1:10023, permit

You must also add some material to /etc/postfix/master.cf, and here is the entire file for clarity, including much of the default material from the package install – such as commented options:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
#
# Postfix master process configuration file.  For details on the format
# of the file, see the master(5) manual page (command: "man 5 master").
#
# 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 on port 25, unencrypted.
smtp      inet  n       -       -       -       -       smtpd
#smtp      inet  n       -       -       -       1       postscreen
#smtpd     pass  -       -       -       -       -       smtpd
#dnsblog   unix  -       -       -       -       0       dnsblog
#tlsproxy  unix  -       -       -       -       0       tlsproxy
# SMTP with TLS on port 587. Currently commented.
#submission inet n       -       -       -       -       smtpd
#  -o syslog_name=postfix/submission
#  -o smtpd_tls_security_level=encrypt
#  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_enforce_tls=yes
#  -o smtpd_client_restrictions=permit_sasl_authenticated,reject_unauth_destination,reject
#  -o smtpd_sasl_tls_security_options=noanonymous
# SMTP over SSL on port 465.
smtps     inet  n       -       -       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_tls_auth_only=yes
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject_unauth_destination,reject
  -o smtpd_sasl_security_options=noanonymous,noplaintext
  -o smtpd_sasl_tls_security_options=noanonymous
#628       inet  n       -       -       -       -       qmqpd
pickup    fifo  n       -       -       60      1       pickup
  -o content_filter=
  -o receive_override_options=no_header_body_checks
cleanup   unix  n       -       -       -       0       cleanup
qmgr      fifo  n       -       n       300     1       qmgr
#qmgr     fifo  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}
# The next two entries integrate with Amavis for anti-virus/spam checks.
amavis      unix    -       -       -       -       3       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
# Integration with Dovecot - hand mail over to it for local delivery, and
# run the process under the vmail user and mail group.
dovecot      unix   -        n      n       -       -   pipe
  flags=DRhu user=vmail:mail argv=/usr/lib/dovecot/dovecot-lda -d $(recipient)

Note that Amavis is restricted to three processes, which should be fine for most casual to moderate use. The processes are memory-heavy, so start low and add more only if you need to due to volume of mail – see the notes in this guide for pointers on how to do that.

17) Restart Everything, and Test the Server

Restart all the necessary processes to pick up configuration changes:

1
2
3
4
5
service postfix restart
service spamassassin restart
service clamav-daemon restart
service amavis restart
service dovecot restart

Now start testing! Keep an eye on /var/log/mail.err and /var/log/mail.log for error messages and try logging in to POP and IMAP, sending mail to an account created on the server, and sending mail from the server. If you find issues, then Google is your friend when it comes to searching on specific error messages in order to identify where the configuration is wrong, or when something unexpected crops up.

18) AWS Mail Restrictions and Reverse DNS Lookup

Once configured, with IP address set and DNS records set up, you’ll need to have a reverse DNS lookup put in place for your server, and the AWS outgoing mail restrictions lifted. You do that through the standard customer service form. This doesn’t take long, and it can actually happen earlier in the process if necessary, prior to the server completion.

 

22) Install and Set up Monit for Monitoring

Monit is a very useful monitoring tool that helps rescue your server from failed processes. Install it through apt-get:

1
apt-get install monit

The following are a set of fairly trivial instructions that set monit to watch over the important server processes – but without issuing notifications or doing much more than restarting on failure. Note that the Amavis configuration specifies a fairly infrequent check; it’s possible to get into a situation with Amavis where it refuses connections because you’re sending mail too rapidly and it hits the server’s maximum number of concurrent connections per process (which is set at a low 128 for Ubuntu). Having Monit then restart it at that point just makes things worse, boosting load and slowing things down. Mail will be queued and reattempted for any period while Amavis is truly down and waiting on Monit to restart it.

Create the following files in the Monit configuration directory.

In /etc/monit/conf.d/amavis:

1
2
3
4
5
6
7
check process amavisd with pidfile /var/run/amavis/amavisd.pid
  every 5 cycles
  group mail
  start program = "/etc/init.d/amavis start"
  stop  program = "/etc/init.d/amavis stop"
  if failed port 10024 protocol smtp then restart
  if 5 restarts within 25 cycles then timeout

In /etc/monit/conf.d/apache2:

1
2
3
4
5
6
7
8
check process apache2 with pidfile /var/run/apache2.pid
  group www
  start program = "/etc/init.d/apache2 start"
  stop program = "/etc/init.d/apache2 stop"
  if failed host localhost port 80 protocol http
    with timeout 10 seconds
    then restart
  if 5 restarts within 5 cycles then timeout

In /etc/monit/conf.d/dovecot:

1
2
3
4
5
6
7
check process dovecot with pidfile /var/run/dovecot/master.pid
  group mail
  start program = "/etc/init.d/dovecot start"
  stop program = "/etc/init.d/dovecot stop"
  group mail
  if failed port 993 type tcpssl sslauto protocol imap for 5 cycles then restart
  if 3 restarts within 5 cycles then timeout

In /etc/monit/conf.d/mysql:

1
2
3
4
5
6
check process mysqld with pidfile /var/run/mysqld/mysqld.pid
  group database
  start program = "/etc/init.d/mysql start"
  stop program = "/etc/init.d/mysql stop"
  if failed host localhost port 3306 protocol mysql then restart
  if 5 restarts within 5 cycles then timeout

In /etc/monit/conf.d/memcached:

1
2
3
4
5
6
check process memcached with pidfile /var/run/memcached.pid
  group www
  start program = "/etc/init.d/memcached start"
  stop program = "/etc/init.d/memcached stop"
  if failed host localhost port 11211 then restart
  if 5 restarts within 5 cycles then timeout

In /etc/monit/conf.d/postfix:

1
2
3
4
5
6
check process postfix with pidfile /var/spool/postfix/pid/master.pid
  group mail
  start program = "/etc/init.d/postfix start"
  stop  program = "/etc/init.d/postfix stop"
  if failed port 25 protocol smtp then restart
  if 5 restarts within 5 cycles then timeout

In /etc/monit/conf.d/spamassassin:

1
2
3
4
5
check process spamassassin with pidfile /var/run/spamd.pid
  group mail
  start program = "/etc/init.d/spamassassin start"
  stop  program = "/etc/init.d/spamassassin stop"
  if 5 restarts within 5 cycles then timeout

In /etc/monit/conf.d/sshd:

1
2
3
4
5
check process sshd with pidfile /var/run/sshd.pid
  start program "/etc/init.d/ssh start"
  stop program "/etc/init.d/ssh stop"
  if failed host 127.0.0.1 port 22 protocol ssh then restart
   if 5 restarts within 5 cycles then timeout

Then restart Monit to pick up the new orders:

1
service monit restart

Monit offers options for notifications, a web console, restarting on high load, logging activity, and many other amenities, so you may want to add more to this very basic configuration.

Notes on Serving Multiple Domains

You can create multiple domains in Postfix Admin if so desired, under Domain List -> New Domain. If you want to use this mail server for more than one domain, you must (a) add the domains in Postfix Admin, and (b) consider whether or not to create domain-specific configuration files for Horde.

Additional domains added in Postfix Admin can be aliased to existing domains (under Virtual List -> Add Alias Domain), such that address@example1.com is always forwarded to address@example2.com, or they can stand as distinct domains with their own accounts, forwards, and so forth.

Depending on your use case, you might also want to adjust some of the .htaccess rules to support users accessing the site at mail.example1.com, mail.example2.com, and so forth – such as expanding the redirect to SSL to recognize all of the domains used.

Horde should work for multiple domains with just the one configuration file, but this may not be optimal for your usage. Try it and see. If not, then you will have to create parallel Horde configuration files for each domain you are using. See the Horde documentation for more on this, as well as the notes for $conf[vhosts] in the Horde configuration web interface.

Notes on Managing Quotas

If you’ve been following carefully, you’ll note that nothing has been said so far on the matter of user disk space quotas – it was not an important goal for the work that prompted the creation of these instructions. As things stand the necessary fields for quota managment exist in the MySQL database but are not used, as (a) the quota module isn’t enabled by default in Dovecot, and (b) Postfix Admin is set not to use quotas by default.

So if you want to enable disk quotas, first alter the Postfix Admin quota configuration in/var/www/postfixadmin/config.inc.php:

1
2
3
4
5
// Quota
// When you want to enforce quota for your mailbox users set this to 'YES'.
$CONF['quota'] = 'YES';
// You can either use '1024000' or '1048576'
$CONF['quota_multiplier'] = '1024000';
1
2
3
4
5
6
7
8
9
10
11
12
// Optional:
// Show used quotas from Dovecot dictionary backend in virtual
// mailbox listing.
// See: DOCUMENTATION/DOVECOT.txt
//
$CONF['used_quotas'] = 'YES';
// if you use dovecot >= 1.2, set this to yes.
// Note about dovecot config: table "quota" is for 1.0 & 1.1,
// table "quota2" is for dovecot 1.2 and newer
$CONF['new_quota_table'] = 'YES';

Next, you will want to enable and configure the quota and imap_quota modules in Dovecot. The former manages quotas while the latter enables reporting on quotas via IMAP. You will want to look through the following documentation for instructions on how to do this:

These configuration changes will be made in 10-mail.conf and 90-quota.conf in the /etc/dovecot/conf.d folder.

Bypassing Spam and Virus Checks for Local Mail

If you’re in the business of sending out newsletters or frequent updates from local software where you completely control the content in those emails, then you probably don’t want to run spam and virus checks for those items. It’s a pointless use of server processing cycles, and a newsletter run can hammer the server if you are making it process the full range of checks on each and every one of those mails.

To have amavisd-new skip the checks for mail originating from a known set of IP addresses (e.g. locally, from a web application on another server, etc), edit /etc/amavis/conf.d/50-user to add these lines:

1
2
3
4
5
6
7
8
9
10
# Replace 111.111.111.111/32 with your desired list of client IP address
# ranges which will bypass checks.
@mynetworks = qw( 127.0.0.0/8 [::1] 111.111.111.111/32 );
# Rules for clients defined in @mynetworks
$policy_bank{'MYNETS'} = { 
  bypass_spam_checks_maps   => [1],  # don't spam-check internal mail
  bypass_banned_checks_maps => [1],  # don't banned-check internal mail
  bypass_header_checks_maps => [1],  # don't header-check internal mail
};

Replace 111.111.111.111/32 with whatever set of IP address ranges you want to bypass amavisd-new checks. All mail arriving from those sources will fall into MYNETS for amavisd-new and therefore bypass checking. If bypassing by IP address doesn’t fit your needs, you can find ways to skip checks for some users, destinations, or sources in a helpful, if dated guide to amavisd-new and Postfix integration.

Some Final Notes on Security

You’ll note that there are a fair number of configuration files that contain database passwords for the mail and Horde data in this server, and that includes PHP files sitting in the webroot. This is not really the dominant security concern: the mail users are virtual and only the server administrator should be logging in as a system user. On AWS the default setup is for SSH login to use keys rather than passwords, and only the ubuntu user has a key setup to allow login. You can also easily lock down the SSH port to selected IP addresses via the security group applied to the server. Further, you can set .htaccess directives to ensure that no web visitor can directly view configuration files – and thus they are only used as includes, which covers the rare case where some error causes PHP files to be served by Apache as plain text. MySQL access is from localhost only, in any case.

All in all the lowest bar from a security perspective is probably that the mail server built here runs a couple of complicated PHP web applications with database access. A serious breach there would involve a way to upload and execute an arbitrary PHP script or shell command with the www-data user’s permissions, or various other XSS attacks allowing for session hijacking of administrators – either way, or just by getting into the mail and Horde databases, compromise of the webroot is compromise of all of the important functions of the server. Horde has had multiple vulnerabilities in past years, but at some point you have to pick your software. On the whole which given the choice I’d rather go with the output of established development communities whose members have a demonstrated track record of vulnerabilities found and fixed, and where there are a large number of eyes directed at the codebase.

These are all good reasons for setting up your webmail on a different server from the one running Postfix and Dovecot – something to bear in mind.

Of course being on AWS – or indeed pretty much any sort of easily available hosting in the US wherein the server is not in your front room – means that the US government has free access to your data any time they particularly feel up to the task, and you may never know a copy was taken. One of the welcome forthcoming evolutions in virtual hosting services will be some form of turn-key encrypted server operations such that you can have the convenience of an AWS-style service but without the transparency it affords the present day panopticon-in-the-making.

Further, it is apparently the case that all email traffic between mail servers is being recorded by various governmental agencies. Unfortunately the present state of SMTP in the wild is that many or most mail servers do not implement the ability to pass emails over an encrypted connection: so while it’s easy to connect to your mail server via POP, IMAP, or a webmail interface with encryption, the email traffic between servers is often plain text. Forcing your server to only use encrypted connections with other servers will mean that a large fraction of your email traffic in both directions will be rejected or unsent. Thus the configuration provided for Postfix in this post is for optional encryption – emails sent and received will be encrypted if the mail server on the other end of the connection can support it.

 Leave a Reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

(required)

(required)