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PostfixVirtualMailBoxClamSmtpHowto

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Postfix 虚拟邮箱和病毒过滤指南

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Introduction(介绍)

In this setup you will be running a small to medium sized email server with Postfix virtual mailboxes for Separate domains and non-Linux Accounts. I do not intend teach you basic stuff with Postfix here. If you are new to Postfix please work on my PostfixBasicSetupHowto to understand basics and proceed with this howto. Also I will tell you howto integrate with ClamSMTP, an SMTP filter for Postfix and other mail servers that checks for viruses using the ClamAV anti-virus software. It aims to be lightweight, reliable, and simple and easy to configure.

在这个教程中你将学习不使用Linux帐号、利用不同的域名来运行起一个中小型的Postfix虚拟邮件服务器。这不是一篇基础的Postfix教程,如果你是个新手,烦请先阅读学习并理解如何设置一个基础的Postfix邮件服务器

Example Setup(配置说明)

In this howto I assume that your are going to host mails for two example domains. Namely domain1.com and domain2.com. Be ready to replace these with your actual domains.

在这个教程里我假设你将使用domain1.com和domain2.com这两个虚拟域名来运行邮件服务器。如果你愿意,可以使用真实的域名来代替domain1.com和domain2.com。

Install Postfix(安装Postfix)

To install postfix(安装Postfix)

Install the postfix package.

安装Postfix套件

Install mailx package for use as command line mail utility program.

Setting Postfix Support for Maildir-style Mailboxes(为Postfix设置Maildir格式的邮箱)

Maildir is a format for an e-mail spool that does not require file locking to maintain message integrity because the messages are kept in separate files with unique names. A Maildir is a directory (often named Maildir) with three subdirectories named tmp, new, and cur. The subdirectories should all reside on the same filesystem.

Please find out more about Maildir here

请在这里寻找更多关于Maildir格式的说明

sudo  vi /etc/postfix/main.cf

Add the following code segment:

在配置文件中添加以下代码:

home_mailbox = Maildir/

Remove the Line mailbox_command = procmail -a "$EXTENSION". We are not going to use it.

将mailbox_command = procmail -a "$EXTENSION"这一行删除。我们不需要使用它。

Restart Postfix to make changes effect.

重启Postfix激活配置。

sudo  /etc/init.d/postfix restart

Postfix virtual Mailboxes for Separate Domains and Non-Linux Accounts

As a system hosts more and more domains and users, it becomes less desirable to give every user their own Linux system account.

With the Postfix virtual mailbox delivery agent, every recipient address can have its own virtual mailbox. Unlike virtual alias domains, virtual mailbox domains do not need the translation from each recipient addresses into a different address, and owners of a virtual mailbox address do not need to have a Linux system account.

The Postfix virtual mailbox delivery agent looks up the user mailbox pathname, uid and gid via separate tables that are searched with the recipient's mail address. Maildir style delivery is turned on by terminating the mailbox pathname with "/".

Look at the following figure and it will be our directory structure for mailboxes.

attachment:VhostsDomains.png

I suggest you to transfer all domains into virtual mailboxes. Even if you have setup postfix with one domain , we will make that domain a virtual domain. Actually you do not need to do this ,but doing this way you will have well organized mail system , and no need to avoid this. Having Postfix host one real domain and the rest virtual means that you will always need to configure Postfix twice: once for each type of domain.

To do that, let's change our myhostname line in main.cf to read:

myhostname = localhost

Create Virtual Mailbox Owner

In our setup all virtual mailboxes are owned by a fixed uid and gid 5000. If this is not what you want, specify lookup tables that are searched by the recipient's mail address.

To create virtual mailbox group:

sudo groupadd -g 5000 vmail

To create virtual mailbox owner:

sudo useradd -m -u 5000 -g 5000 -s /bin/bash vmail

Open main.cf

sudo vi /etc/postfix/main.cf

==== Setup Postfix to Use Virtual Mailboxes ====(设置Postfix以使用虚拟邮箱)

Then add the following code segment to main.cf
将下面的代码段添加到 main.cf 文件中

virtual_mailbox_domains = /etc/postfix/vhosts
virtual_mailbox_base = /home/vmail
virtual_mailbox_maps = hash:/etc/postfix/vmaps
virtual_minimum_uid = 1000
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000

In the first line, we're using a text file called vhosts. You can actually name this anything you want. Inside this text file will be a simple one-column list of all the domains you are hosting. For example, add your all domains there.
在第一行,我们使用了一个名为“vhosts”的文本文件。你也可以用其他的你想要的名字。在这个文本文件中有一个单栏的列表,其中列出了所有的你所管理的域名。

sudo vi /etc/postfix/vhosts

Add the the following codes:
加入以下代码:

domain1.com
domain2.com

This is my example use your own domains here.
这里是一个例子,请在这里使用你自己的域名。

The next line virtual_mailbox_base specifies the base directory where we shall store all of our mail. Again, you can choose anything you want. In our case it will be our '''vmail''' owners's home directory /home/vmail
下一行virtual_mailbox_base 指明了我们存放所有邮件的基础目录。同样的,这里你也可以选择其他你想要的目录。在我们这个例子中,这个目录是'''vmail''' 所有者的主目录/home/vmail


The third line points to a text file I called '''vmaps'''. This is a two column text file. The first column specifies a virtual email address. The second column specifies that persons mailbox location. Just like with real domain hosting, if you specify a / at the end of the location, it becomes Maildir format. If not, it is mbox. Any way in this howto we use Maildir format.
第三行指向了一个名为 '''vmaps'''的文本文件。在这个文件中有两列。第一列指定了虚拟邮件地址。第二列指定了个人邮箱的位置。正如真实的域名主机一样,如果你在路径的最后写上了/ ,那么这个将是Maildir格式。如果没有写这个/ ,那么这个是mbox。在我们这个帮助文档中,我们使用 Maildir 格式。

Setup this file as in this example:
编辑这个 vmaps 文件:

sudo vi /etc/postfix/vmaps

Format of this file should look like:
文件的格式应该如下:

[email protected]  domain1.com/info/
[email protected]  domain1.com/sales/
[email protected]  domain2.com/info/
[email protected]  domain2.com/sales/

Convert vmaps into a hash file by running:
将 vmaps 转化到 hash 文件:

sudo postmap /etc/postfix/vmaps

Remember to execute the above command every time when you add new map.
每一次添加新的映射后请记住再次运行上面的命令。

Restart Postfix to make changes effect.
重启 Postfix 以使更改生效。

sudo  /etc/init.d/postfix restart

My example config look like the following
这个例子的配置应该如下:

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu/GNU)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
myhostname = localhost
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = $myhostname
mynetworks = 127.0.0.0/8, 10.0.0.0/24
mailbox_size_limit = 0
home_mailbox = Maildir/
virtual_mailbox_domains = /etc/postfix/vhosts
virtual_mailbox_base = /home/vmail
virtual_mailbox_maps = hash:/etc/postfix/vmaps
virtual_minimum_uid = 1000
virtual_uid_maps = static:5000
virtual_gid_maps = static:5000
recipient_delimiter = +
inet_interfaces = all

Test Virtual Mailbox Setup(测试虚拟邮箱的配置)

Remember that the directory structure for a particular user is create when you send he gets his firs mail.

Send a mail for [email protected]

In a terminal you can type:

mail [email protected]

Check the mailbox

cd /home/vmail/domain1/info/new
ls

You see a mail file there. If so, Cheers!!!, you have done it.

Setup Non-Linux Accounts

Now it's time to work on the non-unix accounts.

There are several popular techniques to do this using services such as OpenLDAP or MySQL and mixing that with Courier IMAP. We won't be using any of those. Instead, we're going to be using something much more simple: plain text files.

In order to do this, we'll be using Dovecot. If you've never heard of it, you will now. Dovecot is extremely lightweight, flexible, and from what the author says, secure.

Remember the following command will install Dovecot but removes Courier IMAP/POP3 which if you have installed already them. Take it easy ,let's continue to install it.

Install Dovecot IMAP/POP3 server(安装Dovecot IMAP/POP3服务器)

Install the following packages: dovecot-common dovecot-imapd dovecot-pop3d需要安装的包:dovecot-common dovecot-imapd dovecot-pop3d

Configure Dovecot(配置Dovecot)

You need to setup the dovecot to work with our setup. If your are following my steps , the best is to backup your original dovecot config file and create a one for you getting a copy of my file which I will list here.

Let's backup original config file:

sudo mv /etc/dovecot/dovecot.conf /etc/dovecot/dovecot.conf.orig

Create a new config file and copy my config file into it:

sudo vi /etc/dovecot/dovecot.conf

Copy the following code segment and save the file:

base_dir = /var/run/dovecot/
protocols = imap pop3
log_path = /var/log/dovecot
info_log_path = /var/log/dovecot.info
login_dir = /var/run/dovecot/login
login_chroot = yes
login = imap
login_executable = /usr/lib/dovecot/imap-login
login_user = dovecot
login = pop3
login_executable = /usr/lib/dovecot/pop3-login
valid_chroot_dirs = /var/spool/vmail
default_mail_env = maildir:/home/vmail/%d/%n
imap_executable = /usr/lib/dovecot/imap
pop3_executable = /usr/lib/dovecot/pop3
auth = default
disable_plaintext_auth = no
auth_mechanisms = plain digest-md5
auth_userdb = passwd-file /etc/dovecot/users
auth_passdb = passwd-file /etc/dovecot/passwd
auth_executable = /usr/lib/dovecot/dovecot-auth
auth_user = root
auth_verbose = yes


  • Most of the above config lines are pretty self-explanatory . Few of them I need to explain for your understanding.
  • The line "default_mail_env = maildir:/home/vmail/%d/%n" is particularly important. In our virtual hosting set up, the way we distinguish one user from another is to have them log in with their full email address. For example, when the email account is " [email protected] ", Dovecot does some guessing on its end with your user name. If it just sees something like "info", it set's a variable called "%n"to "info". If it sees " [email protected] ", it will split it up and set "%d" to domain1.com and "%n" to "info". Going off of that, if we replace the variables in this line , we get something like: maildir:/home/vmail/domain1.com/info
  • The lines "auth_userdb == passwd-file /etc/dovecot/users" and "auth_passdb == passwd-file /etc/dovecot/passwd" are similar /etc/passwd and /etc/shadow file.

The format of these files goes like this:

/etc/dovecot/users:
[email protected]::5000:5000::/home/vmail/domain1.com/:/bin/false::
/etc/dovecot/passwd:
[email protected]:$1$G/FqlOG5$Vj0xmc9fKY.UVr8OWr/7C1

The 5000:5000 corresponds to the uid and gid of the "virtual" called vmail who owns all the mailboxes in the system . The home directory includes everything but the word before the @ in the email address.

Create Dovecot Users(创建Dovecot用户)

There are no commands like useradd and passwd to add users and passwords for our mail system. I will provide small and quick solution with a bash script. Drawback of my system is that it can not delete users, but you can delete them manually opening the files with vi like ASCII text editor.

没有像"useradd"和"passwd" 这样的命令给我们的邮件系统增加用户及密码. 我将提供一个小巧和快速的脚本来解决. 缺点就是不能删除用户.不过你可以通过使用象"vi"类的文本编辑器来手工删除.

Script to Add Users
增加用户的脚本

Create file: 创建文件:

sudo vi /usr/sbin/adddovecotuser

Add the following code segment and save the file: 增加下面的代码段并保存这个文件:

#!/bin/bash
echo "$1" > /tmp/user
user=`cat /tmp/user | cut -f1 -d "@"`
domain=`cat /tmp/user | cut -f2 -d "@"`
echo "[email protected]$domain::5000:5000::/home/vmail/$domain/:/bin/false::" >> /etc/dovecot/users
# Create the needed Maildir directories
/usr/bin/maildirmake.dovecot /home/vmail/$domain/$user 5000:5000
# To add user to Postfix virtual map file and relode Postfix
echo $1  $domain/$user/ >> /etc/postfix/vmaps
postmap /etc/postfix/vmaps
postfix reload

Make the file executable: 使其可以运行

sudo chmod +x /usr/sbin/adddovecotuser

Add a user like this: 像这样增加用户:

sudo adddovecotuser [email protected]
Script to Set Passwords
设置密码的脚本

First, make sure you have 'mkpasswd' installed: 首先,确认你已经安装了 'mkpasswd':

which mkpasswd

This is not installed by default, and since mkpasswd comes with the 'whois' package, you may have to install this first: 默认状况下是没有安装. mkpasswd 包含在 'whois' 软件包中, 所以要先安装 whois :

sudo apt-get install whois

Create file: 创建文件:

sudo vi /usr/sbin/mkdovecotpasswd

Add the following code segment and save the file: 增加下面的代码段并保存这个文件

#!/bin/bash
mkpasswd --hash=md5 $2  > /tmp/hash
echo "$1:`cat /tmp/hash`" >> /etc/dovecot/passwd

Make the file executable: 使其可以运行:

sudo chmod +x /usr/sbin/mkdovecotpasswd

Add a user like this: 象这样增加一个用户:

sudo mkdovecotpasswd [email protected] password

Replace password with a good password 用一个健壮的密码替换 password

Restart Dovecot to make changes effect 重启 Dovecot 使修改生效

Let's remove world readable permission from password file for security: 清除密码文件的读取权限

sudo chmod 640 /etc/dovecot/passwd

To start Dovecot for the first time 首次启动 Dovecot

sudo /etc/init.d/dovecot start

Testing Your Setup(测试你的配置)

Let's test our system before going production

Testing Dovecot POP3 Server(测试Dovecot POP3服务器)

Type in a terminal 在控制台输入

telnet mail.domain1.com 110

An output like the following will display in your terminal

Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.

Type the following code segment in the prompt provided by the Dovecot POP3 server

user [email protected]
pass password
quit

Final output should be something like this

Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.
user [email protected]
+OK
pass password
+OK Logged in.
quit
+OK Logging out.

Testing Dovecot IMAP Server(测试Dovecot IMAP服务器)

Type in a terminal 在控制台输入

telnet mail.domain1.com 143

An output like the following will display in your terminal

Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.

Type the following code segment in the prompt provided by the Dovecot IMAP server.

a login [email protected] password
a logout

Final output should be something like this

Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.
a login [email protected] password
a OK Logged in.
a logout
* BYE Logging out
a OK Logout completed.

ClamSMTP SMTP Virus Filter

ClamSMTP is an SMTP filter that allows you to check for viruses using the ClamAV anti-virus software. It accepts SMTP connections and forwards the SMTP commands and responses to another SMTP server. The 'DATA' email body is intercepted and scanned before forwarding.

ClamSMTP aims to be lightweight, reliable, and simple rather than have a myriad of options. It's written in C without major dependencies.

ClamSMTP can also be used as a transparent proxy to filter an entire network's SMTP traffic at the router.

Installing ClamAV(安装ClamAV)

We need ClamAV daemon to work with ClamSMTP. Let's install ClamAV first, with the following packages: clamav-daemon clamav

Installing ClamSMTP(安装ClamSMTP)

You need to install the clamsmtp package.

Setting Postfix to use ClamSMTP

Postfix supports filtering mail through a filter that acts like an SMTP server. Put the following lines in your Postfix main.cf file:

Open the file:

sudo vi /etc/postfix/main.cf

If you have doubt where to add the codes look at my example main.cf file

Add the codes:

content_filter = scan:127.0.0.1:10026
receive_override_options = no_address_mappings

The content_filter tells Postfix to send all mail through the service called 'scan' on port 10026. We'll set up clamsmtpd to listen on this port later.

Next we add the following to the Postfix master.cf file:

Open the file:

sudo vi /etc/postfix/master.cf

If you have doubt where to add the codes look at my example master.cf file

Add the codes:

# AV scan filter (used by content_filter)
scan      unix  -       -       n       -       16      smtp
-o smtp_send_xforward_command=yes
# For injecting mail back into postfix from the filter
127.0.0.1:10025 inet  n -       n       -       16      smtpd
-o content_filter=
-o receive_override_options=no_unknown_recipient_checks,no_header_body_checks
-o smtpd_helo_restrictions=
-o smtpd_client_restrictions=
-o smtpd_sender_restrictions=
-o smtpd_recipient_restrictions=permit_mynetworks,reject
-o mynetworks_style=host
-o smtpd_authorized_xforward_hosts=127.0.0.0/8

Make sure there's no spaces around the equal signs or commas in the text you added. Best way is to copy and my codes here.

The first 2 lines create the scan service. The rest set up a service for accepting mail back into postfix. All the options prevent a mail loop as well as relax address checking and the like, since that's already been done.

Make sure to run it as the same user as you run clamd or they'll have problems accessing each other's temporary files. You can use the the following accomplish that.

sudo adduser clamsmtp clamav

Restart Postfix, ClamSMTP, and ClamAV Daemon to make your changes effect:

sudo /etc/init.d/postfix restart
sudo /etc/init.d/clamsmtp restart
sudo /etc/init.d/clamav-daemon restart

Test ClamSMTP for outgoing mail

We need to test the our outgoing mail for viruses. Best way is to download eicar test virus and attach to a mail and send. Let's do it.

Download eicar to you home directory:

wget http://eicar.org/download/eicar_com.zip

Send this file as an attachment to [email protected]

Then check your mail.log file:

tail /var/log/mail.log

You should see something like in your log file.

Mar  8 17:12:02 localhost clamsmtpd: 100004: [email protected], [email protected], status=VIRUS:Eicar-Test-Signature
Mar  8 17:12:02 localhost postfix/smtp[15634]: 4A6C852110: to=<[email protected]>, relay=127.0.0.1[127.0.0.1], delay=0, status=sent (250 Virus Detected; Discarded Email)

Test ClamSMTP for incoming Mail from the Internet

If you have an actual production mail server you can check your mail server for virus provided by webmail.us. They are sending you harmless test mails with the EICAR virus test signature. Also you can use GFI Security Labs for further testing.

Final thoughts

As I said in the beginning this setup is for a small/medium scale company which has few hundred of mail accounts. This doesn't mean that this system is poorly performing. This setup can handle thousands of account with out any performance issue. What I say is here that we need something more manageable like MySQL/PostgreSQL backend for users, web-based virtual domain management, password modifications by users, etc in a extensible, scalable and robust manner.

Hope I have done something for you and Ubuntu.

Yet another howto by: ChinthakaDeshapriya.