Postfix 完整虚拟邮件系统指南

Abstract

There are many howtos in the Internet about setting up mail servers and various people has various choice of MTAs. Some like, Qmail, while some like Postfix or Exim. I have been using Qmail for a long time and it is an excellent MTA. The way the Qmail is licensed and distributed that there are no binary packages so that users can easily setup with their favorite distribution, and installing basic Qmail setup even is not that difficult but users need applied various patches and tweaks etc to get a complete setup done. With all these issues Qmail is the preferred choice of many geeks, since it won't give you head ache once up and running. The drawback is that this system is difficult to upgrade since users need to compile the source code and install.

The decision behind this guide is to use Postfix,an equally secure and fast MTA like Qmail, it is easy to configure and setup a Basic System in any Linux distribution. Postfix has many add-ons and support Maildir format, PostgreSQL and MySQL backend for storing and managing virtual domains very easily. This setup will be a complete virtual mail domain systems , with anti-virus and spam filtering for ISPs , hosting companies, and individual corporations who wish to use Ubuntu Linux as there preferred server platform.

System Overview

It is important to know how our system works before going to install. A virtual mail system needs to be able to handle email for numerous domains with multiple users over a variety of interfaces. When you handle multiple domains within the same mail system it presents you some management issues. We have to answer these issues using our technology. Assume ,for example you may have following questions to answer.

What will you do if you have two users which require same username for different domains?

If you are providing imap access and smtp-auth, how do combine the various authentication daemons into a single system?

How do you provide security for the numerous components that comprise the system?

What we can do, if users are asking their own spam filtering policies.

Individual domain administrators are asking a web-based interface to manage their mail domains

How do you setup a web-based management system for Postfix?

Each user needs a web-base interface to change his mail account's password

How you are going backup user account database and disaster recovery?.

Utilizing ssl for transport layer security

Handle mailing lists for any domain

How do you manage all these issues together?

Don't be panic, I will answer all these questions one by one. Be happy and continue to read this howto.

What You Get

Web based system administration
Unlimited number of domains
Virtual mail users without the need for shell accounts
Domain specific user names
Mailbox quotas
Web access to email accounts
Web base interface to change user passwords
IMAP and POP3 support
Auto responders
SMTP Authentication for secure relaying
SSL for transport layer security
Strong SPAM filtering
Anti-Virus filtering
Log Analysis

Packages Required

The following packages are need to implement our system and most of these packages are in APT repositories. In our installation section you will learn how to install and configure each.

The Big Picture

The following figure shows the big picture of our setup. If you look at it carefully the figure itself is self explanatory.

attachment:CompleteSetupOverview.png

In our setup:

Postfix Mail Transfer Agent receives emails via the SMTP protocol and delivers them to different places on your hard disk.

MySQL database server stores the information to control the behavior of postfix. It knows about users, domains, email forwarding and passwords.

Courier is a standalone mail server just like Postfix but we just use its POP3/IMAP server component to let users access the mailboxes.

SASL, the Cyrus library is using to authenticate your users who are dialed in at another ISP while they are on the road they get an IP address outside of your network. Your mail server however only trusts local IP addresses. The SASL ,Simple Authentication and Security Layer, adds authentication to SMTP and makes your mail server trust them.

How Postfix Mappings Work?

It is very important to how Postfix mapping works. Heart of our system is Postfix mapping. Let's discuss it here. Don't skip this section.

The generic literal meaning of mapping is assign one value to another. What we have to map in Postfix is email user accounts or email address. One example is /etc/aliases, the local aliases or local system users mapping file used by Postfix. The syntax of this file is:

postmaster: root

This makes all the mails which are coming to [email protected] are redirected to [email protected]. We can divide the above syntax to Left Hand Side LHS and Right Hand Side RHS. This RHS and LHS are common abbreviations which we usually used in mappings. The following table will make this idea even more clear.

LHS	RHS
postmaster:	root

attachment:IconHint.png

Usually we do not use colon(:) in LHS for Postfix and this has been done for backward compatibility with historical reasons. The local alias file is a special file that is compiled with newaliases command but not with usual Postfix mapping command postmap

With a basic default Postfix installation we use text file for mappings. We write the mappings into this file and then convert it into a hash file using postmap command. For example, assume that we need to map our virtual mailboxes in a file called /etc/Postfix/virtual_mailboxes. The syntax of this file look like:

[email protected] sigiri
[email protected] kala

You may have noticed that we don't have colon(:) in the LHS of the mappings file

Then you need to run:

postmap /etc/postfix/virtual_mailboxes

You can access this mappings in the Postfix configuration file using the code:

virtual_mailbox_maps=hash:/etc/postfix/virtual_mailboxes

In our setup , we will replace this text mapping files by PostgreSQL tables. Our intention is to make data handling lot more flexible, robust, and scalable. But as database tables usually contain more than just two columns you will need to tell Postfix which column is meant to be the LHS and which is the RHS. For same virtual_mailbox file can be defined in a text file 'like this:

user = postfix
password = YJiNLQtubgnOE
hosts = localhost
dbname = postfix
table = mailbox
select_field = maildir
where_field = username
#additional_conditions == and active == '1'

Let's assume that we save this data in a file called /etc/postfix/mysql_virtual_mailbox_maps.cf.

You can use this mappings in postfix using the following entry in main.cf file.

virtual_mailbox_maps = mysql:/usr/local/etc/postfix/pgsql_virtual_mailbox_maps.cf

The LHS of the mapping is defined as where_field and the RHS is defined as select_field. In this example we will map the

maildir

column to the username column. The other fields in this definition file are user that needs to connect to the PostgresSQL database, password that MySQL user, dbname, the name of the MySQL database, table ,the name of the table in PostgreSQL database and hosts, the name of the server that MySQL runs on. The following tables may clear the idea even more better.

LHS	RHS
select_filed	where_filed
maildir	username

Other fields:

Database User	Database User's Password	Database Name	Database Table	Database Host
postfix	YJiNLQtubgnOE	postfix	mailbox	localhost

How Postfix Virtual Domains Work?

Understanding how virtual domains work is very important to understand how our virtual mail setup works.

There are two types of domains in Postfix.

Local domains: All domains which are listed as mydestination are treated as local domains by Postfix. Emails for local domains are delivered to system users which are listed in /etc/passwd file and these mails are spooled in /var/mail directory.

Virtual domains: In addition to the local domains Postfix can deliver mails for virtual domains. Not like local domains, Postfix will let us to handle virtual domains in a very flexible manner. The good thing is with virtual domains is that we do not need system account in /etc/passwd for each and every mail account. This provides us a way to handle thousands of mail accounts very easily in our mail server system. The mapping which we discussed above is used to handle mail account information. You can use MySQL, PostgreSQL , or LDAP for the user account management. In our setup we use PostgreSQL backend to manage user accounts of virtual domains.

Postfix handles virtual domains as two different categories and need to understand how they work.

- Virtual alias domains: These domains are used to forward or alias mails from one email address to another email address. Such domains can be used receive mailboxes and store on your hard disk. You do not necessarily need to use virtual alias domains in your setup. Instead we can user virtual_alias_maps even if the domains are not listed as virtual alias domains. The virtual_alias_maps is a general-purpose redirection mapping that works for everything that passes your system including local domains.

- Virtual mailbox domains: Postfix uses these domains to receive mails for users under the domains and store them in the mailboxes on the hard disk. This is parameter which will simply tell Postfix to receive the mails on behalf of the domain and store them in each user's mailbox. The virtual_mailbox_maps mapping is used by Postfix to determine the location of the mailbox on your hard disk. Please remember that you can still use the virtual_alias_maps mapping to forward email to other mailboxes or external email addresses so not every user on that domain must actually have a mailbox but can also just have the email forwarded somewhere else.

attachment:IconHint.png

It is important to understand that a domain is either a virtual alias domain or a virtual mailbox domain or a local domain. If you make a domain a virtual alias domain you will not be able to receive email for that domain on your server. On the contrary you can use the virtual_alias_maps to forward/alias email for both types of domain. So the virtual mailbox domains are generally the more flexible to use.

attachment:IconWarning.png

A domain can either be virtual or local and you can not use one domain in the both of these roles. Please never both. So if you decide you want your default domain be a virtual domain then remove it from the mydestination definition. Just leave it blank or set it to mydestination=localhost. Email addresses like root@localhost would then be delivered to the local root user.

Installing a Ubuntu Server System

In this howto I assume that you already know how to setup a Ubuntu server system. I would suggest you to do a Ubuntu server installation without a GUI. If you want to know more about installation look here

DNS Setup

This how to assumes that you already have at least one valid registered domain with an MX record setup for that domain. Setting up a BIND DNS server can be learned here

Package Installation and Configuration

You will to have install and configure all packages which I have mentioned in the "Package Required" section. Let's deal with one by one.

Postfix Base Server Installation

Here we install Postfix and other packages which Postfix requires connect with a MysQL backend.

Installing Postfix

When you install Postfix I would suggest to select "Internet Site" option.

To install Postfix:

sudo apt-get install postfix

To install postfix documentations:

sudo apt-get install postfix-doc

Installing MySQL map support for Postfix

We need to add MySQL mapping support for Postfix. Hope that you have already read How Postfix Mappings Work? section in this howto.

To install postfix-mysql

sudo apt-get install postfix-mysql

To install MySQL client program

sudo apt-get install mysql-client

To install MySQL server

sudo apt-get install mysql-server

Installing Packages for Client Access and Authentication

We will need to offer our user IMAP/POP3 access. Our setup will offer those using the following packages.

To provide client authentication, install:

sudo apt-get install  courier-authdaemon

To add MySQL support for courier-authdaemon, Install:

sudo apt-get install  courier-authmysql

To provide unencrypted POP3 access, install:

sudo apt-get install courier-pop

To provide SSL-encrypted POP3 access, install:

sudo apt-get install  courier-pop-ssl

To provide unencrypted IMAP access, install:

sudo apt-get install  courier-imap

To provide SSL-encrypted IMAP access , install:

sudo apt-get install courier-imap-ssl

Installing package for SMTP authentication

Our system will allow road-warriors to send email through our server using authenticated SMTP. This will basically stop unauthorized relaying through our mail server. Not only we are authenticating our user's when they are retrieving mails but also we authenticate them when they are sending mails as well.

To provide encrypted authenticated SMTP, install:

sudo apt-get install postfix-tls

This may have already installed with postfix. If so,leave it.

To install Cyrus SASL library

sudo apt-get install libsasl2

To add authentication mechanisms for the SASL library, install:

sudo apt-get install  libsasl2-modules

To add MySQL support authentication mechanisms with the SASL library, install:

sudo apt-get install  libsasl2-modules-sql

To create certificates, install:

sudo apt-get install openssl

Setting MySQL Backend

Now that we have installed packages required to prepare a MySQL backend for Postfix. In this section we will configure MySQL database for Postfix.

Setting MySQL root Password

Please note that MySQL root is different from Linux root account. It is the account which which users can use to get administrative previlege with MySQL database sever. Initiall installation of MySQL has no password fro root account. If you have not setup a password for MySQL root yet, this is the time for you to do so. There are few ways to do the same and I will present two of them here. Please user either one of them.

To set MySQL root in the comand prompt:

sudo mysqladmin -u root password rootpassword

or you can use the following steps to do the same

Type in a terminal

mysql -u root

Then in the mysql prompt type:

mysql>SET PASSWORD FOR 'root'@'localhost' = PASSWORD('rootpasswotd');
mysql>\q

Don't forget set a good password rootpassword

Setting MySQL Database for Impatient Users

The schema is based on the postfixadmin MySQL schema. If you are impatient you can driectly create the tables using following steps.

vi postfixadmin-mysql.sql

Then copy and paste the following script to the above file and save it.

To create the database, type in a terminal.

mysql -u root -p < postfixadmin-mysql.sql

#------------------------------------Start copy-------------------------------------
#
# Postfix Admin
# by Mischa Peters <mischa at high5 dot net>
# Copyright (c) 2002 - 2005 High5!
# License Info: http://www.postfixadmin.com/?file=LICENSE.TXT
#

# This is the complete MySQL database structure for Postfix Admin.
# If you are installing from scratch you can use this file otherwise you
# need to use the TABLE_CHANGES.TXT or TABLE_BACKUP_MX.TXT that comes with Postfix Admin.
#
# There are 2 entries for a database user in the file.
# One you can use for Postfix and one for Postfix Admin.
#
# If you run this file twice (2x) you will get an error on the user creation in MySQL.
# To go around this you can either comment the lines below "USE MySQL" until "USE postfix".
# Or you can remove the users from the database and run it again.
#
# You can create the database from the shell with:
#
# mysql -u root [-p] < DATABASE_MYSQL.TXT

#
# Postfix / MySQL
#
USE mysql;
# Postfix user & password
INSERT INTO user (Host, User, Password) VALUES ('localhost','postfix',password('postfix'));
INSERT INTO db (Host, Db, User, Select_priv) VALUES ('localhost','postfix','postfix','Y');
# Postfix Admin user & password
INSERT INTO user (Host, User, Password) VALUES ('localhost','postfixadmin',password('postfixadmin'));
INSERT INTO db (Host, Db, User, Select_priv, Insert_priv, Update_priv, Delete_priv) VALUES ('localhost', 'postfix', 'postfixadmin', 'Y', 'Y', 'Y', 'Y');
FLUSH PRIVILEGES;
GRANT USAGE ON postfix.* TO postfix@localhost;
GRANT SELECT, INSERT, DELETE, UPDATE ON postfix.* TO postfix@localhost;
GRANT USAGE ON postfix.* TO postfixadmin@localhost;
GRANT SELECT, INSERT, DELETE, UPDATE ON postfix.* TO postfixadmin@localhost;
CREATE DATABASE postfix;
USE postfix;

#
# Table structure for table admin
#
CREATE TABLE admin (
username varchar(255) NOT NULL default '',
password varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (username),
KEY username (username)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Admins';

#
# Table structure for table alias
#
CREATE TABLE alias (
address varchar(255) NOT NULL default '',
goto text NOT NULL,
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (address),
KEY address (address)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Aliases';

#
# Table structure for table domain
#
CREATE TABLE domain (
domain varchar(255) NOT NULL default '',
description varchar(255) NOT NULL default '',
aliases int(10) NOT NULL default '0',
mailboxes int(10) NOT NULL default '0',
maxquota int(10) NOT NULL default '0',
transport varchar(255) default NULL,
backupmx tinyint(1) NOT NULL default '0',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (domain),
KEY domain (domain)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Domains';

#
# Table structure for table domain_admins
#
CREATE TABLE domain_admins (
username varchar(255) NOT NULL default '',
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
KEY username (username)
) TYPE=MyISAM COMMENT='Postfix Admin - Domain Admins';

#
# Table structure for table log
#
CREATE TABLE log (
timestamp datetime NOT NULL default '0000-00-00 00:00:00',
username varchar(255) NOT NULL default '',
domain varchar(255) NOT NULL default '',
action varchar(255) NOT NULL default '',
data varchar(255) NOT NULL default '',
KEY timestamp (timestamp)
) TYPE=MyISAM COMMENT='Postfix Admin - Log';

#
# Table structure for table mailbox
#
CREATE TABLE mailbox (
username varchar(255) NOT NULL default '',
password varchar(255) NOT NULL default '',
name varchar(255) NOT NULL default '',
maildir varchar(255) NOT NULL default '',
quota int(10) NOT NULL default '0',
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (username),
KEY username (username)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Mailboxes';

#
# Table structure for table vacation
#
CREATE TABLE vacation (
email varchar(255) NOT NULL default '',
subject varchar(255) NOT NULL default '',
body text NOT NULL,
cache text NOT NULL,
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (email),
KEY email (email)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Vacation';
#------------------------------------End copy-------------------------------------

Step by Step Database Setup

The users who are wish to setup database step by step can use the following steps and understand what table is using what purpose.

Setting up Database, Users, and Privileges

Connect to MySQL database as root

mysql -u root -p

Then type the following sql commands.

To use MySQL user database:

USE mysql;

To create Postfix user & set password

mysql>INSERT INTO user (Host, User, Password) VALUES ('localhost','postfix',password('postfix'));
mysql>INSERT INTO db (Host, Db, User, Select_priv) VALUES ('localhost','postfix','postfix','Y');

To create Postfix Admin user & set password:

mysql>INSERT INTO user (Host, User, Password) VALUES ('localhost','postfixadmin',password('postfixadmin'));
mysql>INSERT INTO db (Host, Db, User, Select_priv, Insert_priv, Update_priv, Delete_priv) VALUES ('localhost', 'postfix', 'postfixadmin', 'Y', 'Y', 'Y', 'Y');
mysql>FLUSH PRIVILEGES;

To Add Privileges for users:

mysql>GRANT USAGE ON postfix.* TO postfix@localhost;
mysql>GRANT SELECT, INSERT, DELETE, UPDATE ON postfix.* TO postfix@localhost;
mysql>GRANT USAGE ON postfix.* TO postfixadmin@localhost;
mysql>GRANT SELECT, INSERT, DELETE, UPDATE ON postfix.* TO postfixadmin@localhost;

To create and use the database:

mysql>CREATE DATABASE postfix;
mysql>USE postfix;

Create the Table Admin

This table is used create the administrators for our virtual mail system. The admin user will be able create, modify, and delete virtadomain administrators, mailboxes and other administrative tasks in the mail system. Postfix is not using this table.

Copy and paste the sql statement to your mysql> prompt.

CREATE TABLE admin (
username varchar(255) NOT NULL default '',
password varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (username),
KEY username (username)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Admins';

Create the Alias table

Postfix is using the "address" and "goto" column. Courier is not using this table.

attachment:IconHint.png This table can be used for virtual .forward files. This table is nothing more than /etc/aliases that you will find on any *nix OS. Multiple destination email addresses need to be separated by a "," (comma).

Following is the table structure for table alias. Copy and paste the sql statement to your mysql> prompt

CREATE TABLE alias (
address varchar(255) NOT NULL default '',
goto text NOT NULL,
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (address),
KEY address (address)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Aliases';

Create the Domain table

Postfix is using the "domain" and "description" column. Courier is not using this table.

Copy and paste the sql statement to your mysql> prompt

CREATE TABLE domain (
domain varchar(255) NOT NULL default '',
description varchar(255) NOT NULL default '',
aliases int(10) NOT NULL default '0',
mailboxes int(10) NOT NULL default '0',
maxquota int(10) NOT NULL default '0',
transport varchar(255) default NULL,
backupmx tinyint(1) NOT NULL default '0',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (domain),
KEY domain (domain)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Domains';

Create the Domain Admin Table

Table structure for table domain_admins. This table is used to create individual administrators for each virtual domain. Postfix or Courier is not using this table.

Copy and paste the sql statement to your mysql> prompt.

CREATE TABLE domain_admins (
username varchar(255) NOT NULL default '',
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
KEY username (username)
) TYPE=MyISAM COMMENT='Postfix Admin - Domain Admins';

Create the Mailbox Table

Postfix is using the "username" and "maildir" column while Courier is using the "username", "password", "name" and "maildir" column.

Copy and paste the sql statement to your mysql> prompt.

CREATE TABLE mailbox (
username varchar(255) NOT NULL default '',
password varchar(255) NOT NULL default '',
name varchar(255) NOT NULL default '',
maildir varchar(255) NOT NULL default '',
quota int(10) NOT NULL default '0',
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
modified datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (username),
KEY username (username)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Mailboxes';

Create the Log Table

Postfix or Courier is not using this table. Instead this table is used to log the activities of domain administrators and mailbox users.

Copy and paste the sql statement to your mysql> prompt.

CREATE TABLE log (
timestamp datetime NOT NULL default '0000-00-00 00:00:00',
username varchar(255) NOT NULL default '',
domain varchar(255) NOT NULL default '',
action varchar(255) NOT NULL default '',
data varchar(255) NOT NULL default '',
KEY timestamp (timestamp)
) TYPE=MyISAM COMMENT='Postfix Admin - Log';

Create the Vacation Table

Virual Vacation is done with a local shell account that can receive email. The email is then handled by a Perl script which sends the Vacation message back to the sender.

Copy and paste the sql statement to your mysql> prompt.

CREATE TABLE vacation (
email varchar(255) NOT NULL default '',
subject varchar(255) NOT NULL default '',
body text NOT NULL,
cache text NOT NULL,
domain varchar(255) NOT NULL default '',
created datetime NOT NULL default '0000-00-00 00:00:00',
active tinyint(1) NOT NULL default '1',
PRIMARY KEY  (email),
KEY email (email)
) TYPE=MyISAM COMMENT='Postfix Admin - Virtual Vacation';

Setting Postfix MySQL Maps

As specified earlier in this document you need to tell Postfix where the control information is stored in the database. You need to create the following four text files in /etc/postfix for that reason.

Creating Virtual Alias Maps

Postfix will use this file for Virtual Alias Maps and it will use The LHS of the mapping is defined as where_field and the RHS is defined as select_field. In this file it would be a mapping of the address column to the goto column.

sudo vi /etc/postfix/mysql_virtual_alias_maps.cf