查看“Postfix 虚拟邮箱和病毒过滤指南”的源代码



== Introduction ==

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 [[Postfix 基本设置指南]] 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

== Example Setup ==

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.

== Install Postfix ==

'''To install postfix'''

<pre><nowiki>   
sudo apt-get install postfix
</nowiki></pre>

Install mailx package for use as command line '''mail''' utility program. '''mail''' command is installed with this package.

<pre><nowiki>
sudo apt-get install mailx
</nowiki></pre>

== Setting Postfix Support for Maildir-style Mailboxes ==

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 [http://en.wikipedia.org/wiki/Maildir here] 

<pre><nowiki>
sudo  vi /etc/postfix/main.cf
</nowiki></pre>

Add the following code segment:

<pre><nowiki>
home_mailbox = Maildir/
</nowiki></pre>

Remove the Line <code><nowiki> mailbox_command = procmail -a "$EXTENSION"</nowiki></code>. We are not going to use it.

'''Restart Postfix''' to make changes effect.

<pre><nowiki>
sudo  /etc/init.d/postfix restart
</nowiki></pre>


== 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 <code><nowiki>myhostname</nowiki></code> line in main.cf to read:

<pre><nowiki>
myhostname = localhost
</nowiki></pre>

=== 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:'''

<pre><nowiki>
sudo groupadd -g 5000 vmail
</nowiki></pre>

'''To create virtual mailbox owner:'''
<pre><nowiki>
sudo useradd -m -u 5000 -g 5000 -s /bin/bash vmail
</nowiki></pre>

Open <code><nowiki>main.cf</nowiki></code>

<pre><nowiki>
sudo vi /etc/postfix/main.cf
</nowiki></pre>

=== Setup Postfix to Use Virtual Mailboxes ===

Then add the following code segment to <code><nowiki>main.cf</nowiki></code>
<pre><nowiki>
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
</nowiki></pre>

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.

<pre><nowiki>
sudo vi /etc/postfix/vhosts
</nowiki></pre>

Add the the following codes:

<pre><nowiki>
domain1.com
domain2.com
</nowiki></pre>

This is my example use your own domains here.

The next line <code><nowiki>virtual_mailbox_base</nowiki></code> 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 <code><nowiki>'''vmail'''</nowiki></code> owners's home directory <code><nowiki>/home/vmail</nowiki></code>


The third line points to a text file I called <code><nowiki>'''vmaps'''</nowiki></code>. 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.

Setup this file as in this example:

<pre><nowiki>
sudo vi /etc/postfix/vmaps
</nowiki></pre>

Format of this file should look like:

<pre><nowiki>
info@domain1.com  domain1.com/info/
sales@domain1.com  domain1.com/sales/
info@domain2.com  domain2.com/info/
sales@domain2.com  domain2.com/sales/
</nowiki></pre>

Convert vmaps into a hash file by running:
<pre><nowiki>
sudo postmap /etc/postfix/vmaps
</nowiki></pre>

Remember to execute the above command every time when you add new map.


Restart Postfix to make changes effect.

<pre><nowiki>
sudo  /etc/init.d/postfix restart
</nowiki></pre>


My example config look like the following

<pre><nowiki>
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
</nowiki></pre>

=== Test Virtual Mailbox Setup ===

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

Send a mail for info@domain1.com

In a terminal you can type:

<pre><nowiki>
mail info@domain1.com
</nowiki></pre>

Check the mailbox

<pre><nowiki>
cd /home/vmail/domain1/info/new
ls
</nowiki></pre>

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 ===

<pre><nowiki>
sudo apt-get install dovecot-common dovecot-imapd dovecot-pop3d
</nowiki></pre>

=== Configure 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:

<pre><nowiki>
sudo mv /etc/dovecot/dovecot.conf /etc/dovecot/dovecot.conf.orig
</nowiki></pre>

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

<pre><nowiki>
sudo vi /etc/dovecot/dovecot.conf
</nowiki></pre>

Copy the following code segment and save the file:

<pre><nowiki>
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
</nowiki></pre>

----
'''Note:''' 
If you are using/testing with Dapper Drake (Ubuntu 6.04), please use [https://wiki.ubuntu.com/DovecotDapperConf Dovecot config file for Dapper ]
----

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 '''"info@domain1.com"''',  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 '''"info@domain1.com"''', 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:'''

::

<pre><nowiki>
/etc/dovecot/users:
info@domain1.com::5000:5000::/home/vmail/domain1.com/:/bin/false::
</nowiki></pre>

<pre><nowiki>
/etc/dovecot/passwd:
info@domain1.com:$1$G/FqlOG5$Vj0xmc9fKY.UVr8OWr/7C1
</nowiki></pre> 

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 ===

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. 

==== Script to Add Users ====

Create file:

<pre><nowiki>
sudo vi /usr/sbin/adddovecotuser 
</nowiki></pre>

Add the following code segment and save the file:

<pre><nowiki>
#!/bin/bash
echo "$1" > /tmp/user
user=`cat /tmp/user | cut -f1 -d "@"`
domain=`cat /tmp/user | cut -f2 -d "@"`
echo "$user@$domain::5000:5000::/home/vmail/$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

</nowiki></pre>

Make the file executable:

<pre><nowiki>
sudo chmod +x /usr/sbin/adddovecotuser 
</nowiki></pre>

Add a user like this:

<pre><nowiki>
sudo adddovecotuser info@domain1.com
</nowiki></pre>

==== Script to Set Passwords ====

First, make sure you have 'mkpasswd' installed:
<pre><nowiki>
which mkpasswd
</nowiki></pre>

This is not installed by default, and since mkpasswd comes with the 'whois' package, 
you may have to install this first:
<pre><nowiki>
sudo apt-get install whois
</nowiki></pre>

Create file:

<pre><nowiki>
sudo vi /usr/sbin/mkdovecotpasswd 
</nowiki></pre>

Add the following code segment and save the file:

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

Make the file executable:

<pre><nowiki>
sudo chmod +x /usr/sbin/mkdovecotpasswd 
</nowiki></pre>

Add a user like this:

<pre><nowiki>
sudo mkdovecotpasswd info@domain1.com password
</nowiki></pre>

Replace '''password''' with a good password

Restart Dovecot to make changes effect

Let's remove world readable permission from password file for security:

<pre><nowiki>
sudo chmod 640 /etc/dovecot/passwd
</nowiki></pre>

To start Devecot for the first time

<pre><nowiki>
sudo /etc/init.d/dovecot start
</nowiki></pre>

== Testing Your Setup ==

Let's test our system before going production

=== Testing Dovecot POP3 Server ===

Type in a terminal

<pre><nowiki>
telnet mail.domain1.com 110
</nowiki></pre>

An output like the following will display in your terminal

<pre><nowiki>
Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.
</nowiki></pre>

Type the following code segment in the prompt provided by the Dovecot POP3 server
<pre><nowiki>
user info@domain1.com
pass password
quit
</nowiki></pre>

Final output should be something like this

<pre><nowiki>
Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.
user info@domain1.com
+OK
pass password
+OK Logged in.
quit
+OK Logging out.

</nowiki></pre>

=== Testing Dovecot IMAP Server ===

Type in a terminal

<pre><nowiki>
telnet mail.domain1.com 143
</nowiki></pre>

An output like the following will display in your terminal

<pre><nowiki>
Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.
</nowiki></pre>

Type the following code segment in the prompt provided by the Dovecot IMAP server.
<pre><nowiki>
a login info@domain1.com password
a logout
</nowiki></pre>

Final output should be something like this

<pre><nowiki>
Trying 69.60.109.217...
Connected to mail.domain1.com.
Escape character is '^]'.
+OK dovecot ready.
a login info@domain1.com password
a OK Logged in.
a logout
* BYE Logging out
a OK Logout completed.
</nowiki></pre>

== 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 ===

We need ClamAV daemon to work with ClamSMTP. Let's install ClamAV first

<pre><nowiki>
sudo apt-get install clamav-daemon clamav
</nowiki></pre>

=== Installing ClamSMTP ===

<pre><nowiki>
sudo apt-get install clamsmtp
</nowiki></pre>

=== 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:

<pre><nowiki>
sudo vi /etc/postfix/main.cf 
</nowiki></pre>

If you have doubt where to add the codes look at my example [https://wiki.ubuntu.com/PostfixClamSmtpMainCf main.cf] file

Add the codes:

<pre><nowiki>
content_filter = scan:127.0.0.1:10026
receive_override_options = no_address_mappings
</nowiki></pre>

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:

<pre><nowiki>
sudo vi /etc/postfix/master.cf
</nowiki></pre>

If you have doubt where to add the codes look at my example [https://wiki.ubuntu.com/PostfixClamSmtpMasterCf master.cf] file

Add the codes:

<pre><nowiki>
# 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
</nowiki></pre>



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.

<pre><nowiki>
sudo adduser clamsmtp clamav
</nowiki></pre>

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

<pre><nowiki>
sudo /etc/init.d/postfix restart
sudo /etc/init.d/clamsmtp restart
sudo /etc/init.d/clamav-daemon restart
</nowiki></pre>

== 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:

<pre><nowiki>
wget http://eicar.org/download/eicar_com.zip
</nowiki></pre>

Send this file as an attachment to '''info@domain1.com'''

Then check your '''mail.log''' file:

<pre><nowiki>
tail /var/log/mail.log
</nowiki></pre>

You should see something like in your log file.

<pre><nowiki>
Mar  8 17:12:02 localhost clamsmtpd: 100004: from=info@domain1.com, to=info@domain1.com, status=VIRUS:Eicar-Test-Signature
Mar  8 17:12:02 localhost postfix/smtp[15634]: 4A6C852110: to=<info@domain1.com>, relay=127.0.0.1[127.0.0.1], delay=0, status=sent (250 Virus Detected; Discarded Email)
</nowiki></pre>

== 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 [http://www.webmail.us/testvirus webmail.us]. They are sending you harmless test mails with the EICAR virus test signature. Also you can use [http://www.gfi.com/emailsecuritytest/ 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.

----
[[category:CategoryDocumentation]]