Linux How-To: Debian Server, Bind9 DNS and Postfix Mail Relay SPAM Filter

So, MS Exchange has been attacked so many times over the years that it would be stupid to let it just sit out on the internet. Same goes for Microsoft DNS server. I would try as hard as I could to never put a Microsoft Server out on the Internet, or even allow a Microsoft to directly service the Internet. It’s just too risky, and I don’t play dice in certain situations such as these. I would, however, make an exception for hosting an Internet Information Services (IIS) Web Server. There are easy ways to lock down IIS and the OS, perform secure code reviews on the website itself, put reverse proxies in front of the web server (Apache Mod_Security or DotDefender)… the list goes on.

But this isn’t a blog about web services. This blog is about setting up a secure Debian Server to host out a Bind9 DNS server and a Postfix reverse email Proxy. And this really could be split up into two different blogs, but I really think that they belong together because of how intertwined Email services are with DNS. Without DNS, mail would be significantly more difficult. But, DNS is also the problem with a LOT of SPAM. DNS configured improperly causes much of the SPAM that gets through to be seen by end users. Also, with DNS and Postfix running on the same box, the services are speedier and more responsive. We’ll do our best, but I really hope I can just refer people to this setup, because I truly believe that if more people would secure their mail servers and setup DNS properly, we could easily stop MOST SPAM that is out on the Internet from making it to Inbox’s around the world.

And this will be a nice, really long, blog… strap in, people, we’re in for a ride! ๐Ÿ™‚


First things first, we need to start with a fresh install of Debian server. The main reason why I choose to go with Debian server is that:

  • First, it’s exceedingly stable and secure right out of the box. Very little configuration is needed…
  • Second, the creators of Debian don’t make tons of changes and they aren’t on the bleeding edge of new technologies.
  • Third, Debian is super easy to use and the software we need is also super easy to install
  • Lastly, especially for virtualized environments, a full install, using my method, takes a minimum of 512MB RAM and 1.5GB HDD space.



I want to let everyone know here, that whatever I post on my site is things that I truly believe in. The main reason why I believe this process to work so well is that I’ve seen it in action at past employers, I’ve seen the MASSIVE cost savings past on to our customers, and because of all that I’ve implemented this exact same process at home. So basically, I eat my own dog food. I’m not going to tell you all to do something that is in secure or full of shit. My email server is already receiving emails through this Postfix Proxy, my domains are hosted off of this BIND9 server, and, if I may say, it’s ALL working beautifully.

A good friend of mine, Nick (I’ll leave out his last name until he says it’s okay to mention him here), was the one who inspired me to get much of this stuff going. I worked with him at a past employer and showed me much of this stuff. Regardless, what I’m trying to get to here is, just the way that we have things setup now is pretty damn good. I have one domain passing all of my mail to a DMZ which has zero restrictions, and that domain forwards all the email it gets to my home server, which is the Proxy we’re about to setup. The reason I do this is to make sure that my SPAM filtering isn’t killing emails I WANT to see. SO, every so often I’ll check both accounts, side by side, and make sure that I’m filtering properly. And if I’m not, I’ll tweak the proxy accordingly. Eventually, maybe even in this blog, I’ll get a mail quarantine up and running so that I can just do away with the DMZ server and pass all my mail through this Proxy…

Lastly, I’ve gone out of my way to make this as absolutely clear as I can. I’ve referenced all the sites and pages at the bottom of this blog, as I always do, and made this as close to perfect as I can. If you want an “installer” for this process, then you’re in the wrong spot. I will never build an automated installer for this without charging a butt load of money. If that’s what you’re looking for, go buy some Windows based software. Here, we’re working with Debian server on the Bash Shell.



Anyways… So let’s get a base image up and running.

Debian Minimal Install: The base for all operations

When you’re done with that come back here and we’ll keep going… In the mean time let’s talk about the software we’re dealing with here…



While Postfix can do a lot, just by itself, in filtering SPAM, it’s not the end all, be all, software. It’s literally just a Mail Transfer Agent (MTA), and it’s only purpose is to send and receive mail. So what we need to do here is arm Postfix with some weaponry, by the likes of Amavis-New, SpamAssassin, Anomy Sanitizer, and ClamAV. Now, I know your thinking, “ClamAV, huh?” But it’s better than nothing, it’s open source and it’s got over a million signatures. If you’re reading this thinking “WTF? My company wont be able to run this!”, then you’re in luck, because Postfix can forward mail for AV inspection to many of the top names in Anti Virus (Kaspersky, Symantec and McAfee). But for this article we’re going to work with ClamAV and some other tools, so deal with it. It’s free, and so is this blog…




Amavis-New is a really good SPAM filtering engine, as well as SpamAssassin. What we’ll have to do is create two directories for Amavis and SpamAssassin to work in. They both receive mail from Postfix, unpack the email and attachments, inspect everything, then package everything back up the way they should be, and send it back to Postfix. This happens in two forks. Amavis gets the email first, then sends it back to Postfix, then it’s sent to SpamAssassin, then sent back to Postfix.

When Amavis first starts at system boot, it just sits there and waits until it gets work to do, as any good little daemon should do. But when an email comes in, Amavis instantly forks a child process to do the work that needs to be done. This child process will create a sub directory in, in the Amavis working directory, and to it’s unpacking, inspection and repacking in. In the Amavis conf file you can specify how many children can be spawned, but you’ll want to test this out. Our config will have 5 children, and on a box with 1GB of ram, we should have PLENTY of room to work with. Now, if you’re running a Enterprise level SPAM filtering service, you may want to setup multiples of these servers that sit on a few or more MX records so that you can spread out the work load. Then beef up how much RAM and CPU cores you allocate to the VM and then allow Amavis to spawn more children. Pending the amount of hardware you have to work with, you could filter a TON of email with this configuration.

Really though, at the end of the day, I strongly recommend that you investigate the Amavis-New website. Their FAQ’s are great and super informative. It’s truly amazing what this product can do.




As for SpamAssassin let’s talk about this for a minute. At the writing of this blog, Spam Assassin is at release 3.3.1. I’ll tell you the same thing I said a minute ago about Amavis: You should really look at the Spam Assassin website for more details about running, installing, configuring, testing and the operations of Spam Assassin. But I’ll briefly go over this stuff now. SpamAssassin works like many other filtering engines, “grading” the email on a multitude of different areas, including content, encoding, MIME settings, HTML markup and blacklists provided from different carriers like Spamhaus (which we’ll talk about later in this blog). Configured and monitored properly, Spam Assassin, just by itself, can filter over 97% of all SPAM, it’s false positive ratio is easily 1% or less, and the best part is that it has the ability to “learn” about new SPAM. The scoring engine is like a game of golf. The lower the score, the better. Other factors are looked at as well, such as Blacklisted IP’s, Reverse DNS lookups, list of banned words, list of banned file attachments (exe, vbs, etc…) sender and receiver addresses, valid date and time, etc…

SpamAssassin isn’t all by itself though. While SpamAssassin is able to do a LOT on it’s own, it also “calls” other programs in to help it, such as razor, pyzor, and dcc-client. Each of these programs have specialized duties that perform additional SPAM checking. Razor is a distributed network devoted to spam detection. Razor uses statistical and randomized signatures that effectively identify many different types of SPAM. Pyzor, not surprisingly, is built on Python and also is based on a network dedicated to identifying SPAM. Like Razor, it too is signature based. Lastly, DCC (Distributed Checksum Clearinghouses) is also an anti-spam content filter. According to the DCC website, “The idea of DCC is that if mail recipients could compare the mail they receive, they could recognize unsolicited bulk mail. A DCC server totals reports of checksums of messages from clients and answers queries about the total counts for checksums of mail messages. A DCC client reports the checksums for a mail message to a server and is told the total number of recipients of mail with each checksum. If one of the totals is higher than a threshold set by the client and according to local whitelists the message is unsolicited, the DCC client can log, discard, or reject the message.”

Back to SpamAssassin… The thing that really makes SpamAssassin great is the way that it handles SPAM. It’s completely configurable to the way YOU want SPAM handled. You can have it tag email as potential SPAM by just changing the email headers. There’s also ways that Spam Assassin will modify the Subject line of an email to include text like “***Potential SPAM***” or whatever you want it to say to your end users. This option truly is great, because there will always be false positives (email marked as SPAM that really isnt), and there will always be false negatives (SPAM that gets through to the end user that shouldn’t). With Subject line modification, we can alert the user to use their best judgement in looking at an email. If a message has a high enough score we can have the message quarantined until the user releases the message for review, or in extreme cases the email can just be dropped without notification.

On the contrary, not all email should be blocked either. And Spam Assassin can look into messages to see if they have good karma. This sounds strange, but while there are services like Spamhaus, there are services that do the exact opposite of them. For instance, there are services like ISIPP Email Accreditation and Deliverability, Return Path who actually owns Bonded Sender which used to be Iron Port‘s product (which now Cisco owns), and more.




Just because I’m too lazy to keep going on with this, I’ll just forward you to the Anomy website and you can look at their information if you want to know more. The main reason why I’ve decided to incorporate Anomy is because of the fact that, while the other SPAM and Virus checkers need to perform inspection on the disk, which can get very intense (and in extremely large environments can cause performance issues), Anomy does everything in system memory. The other reason why is that Anomy comes with it’s own custom built MIME parser which performs more checks than some of the other options. The thing that we’re looking at here is security in layers. You’ll hear that concept driven into your head over and over until the end of time. Security in layers. The day that you can buy 1 product to perform ALL of your security needs is the day I’m out of a job. Until then, you’re going to have to use multiple scan engines, multiple security technologies and continue to drive a culture of knowledge for your employees.




Awesome, you got your VM up and running!!!


SSH and Server Certificates

In that tutorial I had you setup the IP address on your new Debian server to We’ll reference that IP address for the rest of the time, but you can substitute it for whatever you made it on your network.

If you haven’t done this yet, we’re going to make life easy and get the SSH Server installed so we can get some remote access to this server from our Linux Desktop.

apt-get install ssh openssh-server openssh-client


When that’s done test out connecting from your local machine to this virtual host using:

ssh steve@

Now we can setup SSH keys on this system so that you can easily log in from your main Linux Desktop machine.


So go to your home directory on your local machine (NOT THE SERVER!) and your navigate to your home folder. From here CD into your .ssh directory and we’ll create your SSH Certificates.

cd ~/.ssh/
ssh-keygen -t rsa
{save as default file, press enter}        
{enter your own password and hit enter}     <-- this can be blank
{confirm your password}                     <-- this can be blank


Once this is done we’ll setup your host with keys to stay authenticated

cat ~/.ssh/ | ssh steve@ "cat - >> ~/.ssh/authorized_keys"


Now edit your “.ssh/config” file and add in your new server. If you dont have one just create one!

Host 100
User steve


And now you can test your new ssh keys by doing this:

ssh 100


You may need to adjust your permissions properly. To do so, simply run this command on your local system:

chmod 700 ~/.ssh && chmod 600 ~/.ssh/*


And this command on your remote system that you’re trying to connect to:

chmod 600 ~/.ssh/authorized_keys && chmod 700 ~/.ssh/


Disable IPv6

For our install, we need to disable IPv6. I’ve seen issues with Postfix and Bind when there is IPv6 running on the same box. I always bitch about lazy admins, and here I am being lazy and turning off IPv6 instead of fixing the underlying issue. ๐Ÿ™


                           SO! Let’s get IPv6 disabled! haha ๐Ÿ™‚


I promise I’ll look into the issue over time, because I’ll need to make this solution work with IPv6 eventually. I can’t run from it forever. In the mean time, lets get going with editing your grub file:

sudo vim /etc/default/grub


While you’re in your Grub file, find the line that looks like this:



What you need to do here is make it look like this:



Then you need to update the loader by doing this:

steve @ debian ~ :) ?>   sudo update-grub2
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.32-5-amd64
Found initrd image: /boot/initrd.img-2.6.32-5-amd64
steve @ debian ~ :) ?>   sudo update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.32-5-amd64
Found initrd image: /boot/initrd.img-2.6.32-5-amd64



Bind9 Domain Name System (DNS)

Perfect! Now, let’s get Bind9 installed and configured properly. What I’ve done in my network is allowed my Internal Name Servers keep a copy of the External DNS zones. It makes life easier than setting up all your internal servers to also look at your External Servers. We’ll run through that as well during the setup. You’ll also want to get a copy of the Bind 9 Administrator Reference Manual. It’s not critical, but there’s some pretty damn good information in that document. has both the online website and the downloadable PDF document.

sudo apt-get install bind9


Now that Bind is installed, lets configure the service to do what we want. We’ll start by editing our “named.conf” file where all the good stuff is.

cd /etc/bind/
sudo vim named.conf

### Named.conf File ###
// This is the primary configuration file for the BIND DNS server named.
// Please read /usr/share/doc/bind9/README.Debian.gz for information on the
// structure of BIND configuration files in Debian, *BEFORE* you customize
// this configuration file.
// If you are just adding zones, please do that in /etc/bind/named.conf.local

include "/etc/bind/named.conf.options";
include "/etc/bind/named.conf.local";
include "/etc/bind/named.conf.default-zones";


This file is really tiny; it’s really just the spawn point for all the other configurations. And there’s two ways you can do this.

  • 1. You can remove all the other files and just do all your configurations in here
  • 2. You can continue to use the file structure the way it is

Either way will work. If you’re a small company with only a few domain names, you can easily get away with lumping everything into this file and still keep separate zone files. If you’re a large company you may want to stay with many separate, smaller, configuration files. Especially when you’re dealing with companies that own hundreds, if not thousands, of domain names… even more so if you’re dealing with companies dispersed over several continents… or globally!


In this scenario, we’re going to tighten things up just to make the initial config easy to see, but by no means am I telling you that you have to do it this way. DO it however you feel makes the most sense to you!


So here we have the named.conf file; go ahead and make a backup of all your config files into a backup folder here and then modify your named.conf to look like mine below.

cd /etc/bind/
sudo mkdir installer-backup
sudo cp * installer-backup/
rm named.*


And here is the code you can copy and paste into your “named.conf” file:

sudo vim named.conf

#  This is not part of the default configuration that is included as part of the    #
#  Bind 9 package. This section is commented out because it isnt needed.            #
#  Also, for all of the files that were installed by default,                       #
#  look in the "/etc/bind/installer-backup" directory                               #
  #                                                                               #
  #                CONFIGURED BY STEVE ERDMAN, updated 12/27/12                   #
  #                                                                               #

// The following section is the called the options section.
// Configures the working directory for this BIND9 installation
// Sets up BIND to allow query's from the Internet
// recursion only from the Internal network (Change to your Internal Network!)
// Forwarders set to Level 3, Google and OpenDNS public servers (if these guys dont work, the Internet is probably broken!
// Listening on all interfaces (make sure to update this address to your real IP on this server!)
// IPv6 turned off
// running "named" version
// auth-nxdomain states that this server will answer authoritatively for all domains configured on it

options {
        directory "/etc/bind";
        notify-source * port 53;
        allow-query { any; };
        allow-recursion {;; };
        forwarders {;;;;;; };
        listen-on {;; };
        listen-on-v6 { none; };
        version "named";
        auth-nxdomain yes;    # conform to RFC1035
// end of options

#     Below are all of the zone files for all the forward and lookup zones that your    #
#     company is responsible for.                                                       #

// zone name
// 'type' only allows master, slave, stub, forward, hint... We own our zone, we're the master.
// specify the file that our zone sits in
// allow anyone to query our server
// allow our internal name servers to cache this zone as a slave server
// specify that if the zone data may have changed, that all servers with this zone data need to contact the SOA
zone "" IN {
                type master;
                file "/etc/bind/";
                allow-query { any; };
                allow-transfer {;;;; };
                notify yes;
//same options apply as the above zone
// 111.222.333.44 Reverse DNS
zone "" {
                type master;
                file "/etc/bind/";
                allow-query { any; };
                allow-transfer {;;;; };
                notify yes;

#   Consider adding the 1918 zones here, if they are not used in your organization  #
#                  to use these just uncomment the following line:                      #
#   include "/etc/bind/zones.rfc1918";                          #
     #   Below are some zones that your server should cache                        #
     #   The for more info on this visit:     #

// prime the server with knowledge of the root servers
zone "." {
        type hint;
        file "/etc/bind/db.root";
// be authoritative for the localhost forward and reverse zones, and for
// broadcast zones as per RFC 1912
zone "localhost" {
        type master;
        file "/etc/bind/db.local";
zone "" {
        type master;
        file "/etc/bind/db.127";
zone "" {
        type master;
        file "/etc/bind/db.0";
zone "" {
        type master;
        file "/etc/bind/db.255";



Now we need to create some zone files. “What is a zone file?” you may be asking… Well, zone files are where all of your host information is stored, so that when a Internet customer queries “” your DNS server looks up in it’s zone file the “www” host A record, and returns the response. There are all kinds of records, and here is a site that can explain all of this for you: List of DNS record types at Wikipedia.


Now that you’re understanding records, lets get your zone file going. Working off of the example “named.conf” file above, let’s create our “” and “” zone files. If you want to cheat a little bit, go ahead and use a zone file generator such as this one, but you really should understand how they work as well. So let’s look at one…

sudo vim

; BIND data file for
$TTL 3600
@       IN      SOA (
                        201212263453789   ; serial number YYMMDDNN + some numbers
                        28800           ; Refresh
                        7200            ; Retry
                        3600          ; Expire
                        3600           ; Min TTL

    IN  NS
        IN  NS

        IN  MX  10
        IN  MX  20

    IN  A   111.222.333.41
ns1     IN      A       111.222.333.42
ns2     IN      A       111.222.333.43
mail    IN      A       111.222.333.44
smtp    IN      A       111.222.333.45
autodiscover    IN      A       111.222.333.46
vpn     IN      A       111.222.333.47
www     IN      A       111.222.333.48


Now let’s look at our Reverse Lookup zone so you can get an idea of what yours should look like:

sudo vim

; BIND data file for local loopback interface
$TTL 3600
@       IN      SOA (
                        201212263453789   ; serial number YYMMDDNN
                        28800           ; Refresh
                        7200            ; Retry
                        3600          ; Expire
                        3600           ; Min TTL

42     IN      NS
43     IN      PTR
44     IN      PTR
45     IN      PTR
47     IN      PTR
48     IN      PTR


Awesome, now, one last thing that has helped me is if the “/etc/bind/” directory was owned by the “bind” user that was created upon install. Let’s do that real quick!

sudo chown -R bind:root /etc/bind/


Give your Bind server a quick restart, but you restart the service, open another bash shell tab (or session) and do a “sudo tail -f /var/log/syslog” and watch the output to make sure everything loads properly. It all should load up right, but if not, it’s better to find out now if there’s a problem than to wait until the end and troubleshoot tons of errors you *MAY* be having.


sudo /etc/init.d/bind9 restart
Stopping domain name service...: bind9 waiting for pid 2655 to die.
Starting domain name service...: bind9.


And dont forget your “tail”!

steve @ debian ~ :( ?>sudo tail -f /var/log/syslog
[sudo] password for steve:
Dec 26 22:17:01 debian /USR/SBIN/CRON[3353]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Dec 26 22:48:05 debian named[2655]: received control channel command 'stop -p'
Dec 26 22:48:05 debian named[2655]: shutting down: flushing changes
Dec 26 22:48:05 debian named[2655]: stopping command channel on
Dec 26 22:48:05 debian named[2655]: stopping command channel on ::1#953
Dec 26 22:48:05 debian named[2655]: no longer listening on ::#53
Dec 26 22:48:05 debian named[2655]: no longer listening on
Dec 26 22:48:05 debian named[2655]: no longer listening on
Dec 26 22:48:05 debian named[2655]: exiting
Dec 26 22:48:06 debian named[3491]: starting BIND 9.7.3 -u bind
Dec 26 22:48:06 debian named[3491]: built with '--prefix=/usr' '--mandir=/usr/share/man' '--infodir=/usr/share/info'
Dec 26 22:48:06 debian named[3491]: adjusted limit on open files from 1024 to 1048576
Dec 26 22:48:06 debian named[3491]: found 2 CPUs, using 2 worker threads
Dec 26 22:48:06 debian named[3491]: using up to 4096 sockets
Dec 26 22:48:06 debian named[3491]: loading configuration from '/etc/bind/named.conf'
Dec 26 22:48:06 debian named[3491]: reading built-in trusted keys from file '/etc/bind/bind.keys'
Dec 26 22:48:06 debian named[3491]: using default UDP/IPv4 port range: [1024, 65535]
Dec 26 22:48:06 debian named[3491]: using default UDP/IPv6 port range: [1024, 65535]
Dec 26 22:48:06 debian named[3491]: listening on IPv4 interface lo,
Dec 26 22:48:06 debian named[3491]: listening on IPv4 interface eth0,
Dec 26 22:48:06 debian named[3491]: generating session key for dynamic DNS
Dec 26 22:48:06 debian named[3491]: set up managed keys zone for view _default, file 'managed-keys.bind'
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 254.169.IN-ADDR.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 2.0.192.IN-ADDR.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 100.51.198.IN-ADDR.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 113.0.203.IN-ADDR.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone:
Dec 26 22:48:06 debian named[3491]: automatic empty zone:
Dec 26 22:48:06 debian named[3491]: automatic empty zone:
Dec 26 22:48:06 debian named[3491]: automatic empty zone: D.F.IP6.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 8.E.F.IP6.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 9.E.F.IP6.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: A.E.F.IP6.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: B.E.F.IP6.ARPA
Dec 26 22:48:06 debian named[3491]: automatic empty zone: 8.B.D.
Dec 26 22:48:06 debian named[3491]: command channel listening on
Dec 26 22:48:06 debian named[3491]: command channel listening on ::1#953
Dec 26 22:48:06 debian named[3491]: the working directory is not writable
Dec 26 22:48:06 debian named[3491]: zone loaded serial 1
Dec 26 22:48:06 debian named[3491]: zone ending notifies (serial 3289701)
Dec 26 22:48:06 debian named[3491]: zone loaded serial 1
Dec 26 22:48:06 debian named[3491]: zone loaded serial 1
Dec 26 22:48:06 debian named[3491]: zone loaded serial 16381
Dec 26 22:48:06 debian named[3491]: zone localhost/IN: loaded serial 2
Dec 26 22:48:06 debian named[3491]: managed-keys-zone ./IN: loading from master file managed-keys.bind failed: file not found
Dec 26 22:48:06 debian named[3491]: managed-keys-zone ./IN: loaded serial 0
Dec 26 22:48:06 debian named[3491]: running
Dec 26 22:48:06 debian named[3491]: zone sending notifies (serial 598703)



Success! Your DNS server started and all your zones are loaded! Let’s test a couple queries and just make sure ๐Ÿ™‚

steve @ debian ~ :) ?>   dig @ mx

; <<>> DiG 9.8.1-P1 <<>> @ mx
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55227
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 4

;          IN  MX

;; ANSWER SECTION:       3600    IN  MX  20       3600    IN  MX  10

;; AUTHORITY SECTION:       3600    IN  NS       3600    IN  NS

;; ADDITIONAL SECTION:  3600    IN  A  3600    IN  A   3600    IN  A   3600    IN  A

;; Query time: 1 msec
;; WHEN: Wed Dec 26 22:52:11 2012
;; MSG SIZE  rcvd: 172


Fantastic, we’re looking good so far!



Now that you’re mostly updated, you’ll need to visit the registrar for your domain name and update the information for where your domain is hosted. These records are called glue records and normally they take a while to update. They could take up to 12 or 24 hours to update so dont get worried if you have and DNS issues in the next few hours. Really, the best time to update that information for production domains (domains that cant suffer down time) is early on a Saturday night. Many people are watching TV, busy with the family or out on the town after 8pm on a Saturday (unless you’re me, haha). By the time the propagation spreads across the Internet, it’s Sunday morning and no one really noticed. Also, you’ll want to get on the phone with your ISP to have them forward all reverse lookup queries to your name servers. This is critical if you want YOUR out going email not to be tagged as SPAM!

According to WikiPedia, “Name servers in delegations are identified by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. If the name given in the delegation is a subdomain of the domain for which the delegation is being provided, there is a circular dependency. In this case the nameserver providing the delegation must also provide one or more IP addresses for the authoritative nameserver mentioned in the delegation. This information is called glue. The delegating name server provides this glue in the form of records in the additional section of the DNS response, and provides the delegation in the answer section of the response.

For example, if the authoritative name server for is, a computer trying to resolve first resolves Since ns1 is contained in, this requires resolving first, which presents a circular dependency. To break the dependency, the nameserver for the org top level domain includes glue along with the delegation for The glue records are address records that provide IP addresses for The resolver uses one or more of these IP addresses to query one of the domain’s authoritative servers, which allows it to complete the DNS query.”


While your registrar information is updating let’s move forward and get some email action going!


If all you were looking for here was a DNS tutorial for a single DNS server, you’re done. If you’re looking to go any further into SPAM filtering, continue on!

I will be posting a blog as soon as I can on how to setup a distributed DNS server cluster. Stay tuned for that!



Postfix and SPAM Filtering

Alright, we need some software here, so… lets get Postfix installed!

sudo apt-get update && sudo apt-get dist-upgrade
sudo apt-get install -y postfix


Now, when the software is installing, you’ll want to setup Postfix in a certain way. You NEED to make sure you pick “Internet Site” at the first prompt, and enter your EXTERNAL MX A-record. Many times this MX A Record is either “” or”, but you’ll want to verify from your DNS zone that we created back in the BIND9 section.. See my screenshots below:

Internet Site


Now that we have Postfix installed, we can setup a temporary mail relay to our Microsoft Exchange server. THIS SHOULD NOT BE IN PRODUCTION RIGHT NOW!

GO ahead and edit your “” file. There is a line we need to change that I’ll show you below:

sudo vim /etc/postfix/

# Uncomment the next line to generate "delayed mail" warnings
delay_warning_time = 4h

# Add the IP address of your Exchange server's Receive Connector responsible for your Domain. (See below Screenshot)
relayhost =

# And lastly, find "myorigin", and right below that add in "relay_domains =,, (other, domains, comma, separated)"
myorigin = /etc/mailname
relay_domains =,,,

# If you're hosting multiple domains, you'll want to setup a transport config file.
transport_maps = hash:/etc/postfix/transport

WE will talk about the /etc/postfix/transport file, and others, later, but this DOES need to be there!

Exchange Server Receive Connector


Now that we have that complete, we’ll restart the service:

sudo /etc/init.d/postfix restart


SPAM Filtering Engines

Alright, cool… Let’s get some more software installed!

sudo apt-get install -y amavisd-new spamassassin clamav-daemon


As soon as that’s complete you’ll want to update the ClamAV virus definitions. They’re readily available, and even easier, you can run a simple command to do this:

sudo freshclam
[sudo] password for steve:
ClamAV update process started at Thu Dec 27 00:16:40 2012
main.cvd is up to date (version: 54, sigs: 1044387, f-level: 60, builder: sven)
daily.cvd is up to date (version: 16130, sigs: 427971, f-level: 63, builder: neo)
bytecode.cvd is up to date (version: 209, sigs: 40, f-level: 63, builder: neo)

If you’re really looking to have fun with this, just create a quick shell script and then make a cron job out of it to run daily ๐Ÿ™‚


Alright, more software to install. Mainly more dependencies and stuff you’ll need that may not have been installed yet.

sudo apt-get install -y libnet-dns-perl pyzor razor libarchive-tar-perl libio-socket-ssl-perl libio-socket-inet6-perl libnet-ident-perl liburi-perl libwww-perl libmailtools-perl tnef arj bzip2 cabextract cpio file gzip nomarch pax unzip zip zoo ripole cabextract p7zip lzop rpm2cpio unrar-free arc


Perl Script Installs

Following some package installs, we’ll be needing some perl scripts. So to install those, follow these instructions:

steve @ debian ~ :) ?>   sudo perl -MCPAN -e shell

CPAN is the world-wide archive of perl resources. It consists of about
300 sites that all replicate the same contents around the globe. Many
countries have at least one CPAN site already. The resources found on
CPAN are easily accessible with the module. If you want to use, lots of things have to be configured. Fortunately, most of
them can be determined automatically. If you prefer the automatic
configuration, answer 'yes' below.

If you prefer to enter a dialog instead, you can answer 'no' to this
question and I'll let you configure in small steps one thing after the
other. (Note: you can revisit this dialog anytime later by typing 'o
conf init' at the cpan prompt.)
Would you like me to configure as much as possible automatically? [yes]


You’ll see a ton of information fly by as many values are automatically generated for you.
Feel free to look at that stuff if you want. When you’re ready install the perl modules we need:

(as you’re installing these Perl modules, you’ll see a lot of scrollback)

o conf prerequisites_policy ask
o conf commit
install IP::Country::Fast
install MIME::Base64
install MIME::QuotedPrint
install Net::DNS
install DB_File


Now for the DCC install. I haven’t found a package for DCC in the Debian repo’s unfortunately, and while that is a drawback to this software, it’s not the end of the world. We’ll just need to do some quick building of the software. But first we need to acquire the software from the DCC download page. The newest version that is out was released on January 12, 2013.

From your Debian VM, run this command:


Then you can extract and build the software like this:

tar -xzvf dcc-1.3.144.tar.Z
cd dcc-1.3.144/
sudo make install clean

And you’re ready to move forward! (we’ll configure DCC later, for now we just need to have the software installed)


Perfect, we’re moving right along here. One other thing to note here is that with all this going on, you’re going to want a highly tuned box. What I mean by that is, think of it this way: Every time a message comes in, we’re sending that message through 4 scanning engines, each one of which invokes it’s own shell or child process, some using a Perl interpreter, and unpacking/repacking each message in a temporary folder, inspecting the message and then sending it back out to your internal Exchange server. There’s A LOT going on here. This may add a bit of latency to the delivery of your messages. Remember, I’m running a VM on an SSD, with a Core i7 960, and the VM has 2 cores and 1GB of RAM. The latency I’m seeing here, as opposed to my other email service, is less than 1 minute, which is more than reasonable. We’ll go over some tuning at the end of this and tweak this whole system to work as efficiently as possible.


Okay, now we need some user accounts created so that we can tighten up security a bit.

Start by cat’ing your /etc/passwd file. Pending if your following my tutorial on a Red Hat, CentOS, Ubuntu or other OS, I want to make sure that our “amavis”, “spamd”, “anomy” and “clamav” users are created.

steve @ debian ~ :) ?>   cat /etc/passwd
steve:x:1000:1000:Steve Erdman,,,:/home/steve:/bin/bash
amavis:x:107:111:AMaViS system user,,,:/var/lib/amavis:/bin/sh


SpamAssassin Configure

Based on this information, we’re good on most user accounts, but we need to create a “spamd” account and an “anomy” account. We also need to setup working directories for both of these services and lock down access to them.

sudo mkdir /var/run/spamassassin
sudo mkdir /usr/local/anomy
sudo groupadd -g 112 spamd
sudo useradd -u 112 -g 112 -s /sbin/nologin -d /var/run/spamassassin spamd
sudo chown spamd:spamd /var/run/spamassassin
sudo chmod 750 /var/run/spamassassin
sudo groupadd -g 113 anomy
sudo useradd -u 113 -g 113 -s /sbin/nologin -d /usr/local/anomy anomy
sudo chown root:anomy /usr/local/anomy
sudo chmod 750 /usr/local/anomy
sudo usermod -a -G clamav amavis
sudo usermod -a -G amavis clamav


Now let’s modify the SpamAssassin conf file:

sudo vim /etc/default/spamassassin


And modify these parameters: ( by default, SpamAssassin is disabled, we need to give it options to start)

OPTIONS="--username=spamd --create-prefs --max-children 5 --helper-home-dir"


Now lets try to start SpamAssassin:

sudo /etc/init.d/spamassassin restart


And update the databases for SpamAssassin:

sudo sa-update



Amavis-New Configure

Now, let’s get Amavis running. Technically, it is already running, but we need to enable Virus and SPAM filtering. Start by editing this file:

sudo vim /etc/amavis/conf.d/15-content_filter_mode


There are 4 lines in the file that you need to “uncomment”. See below:

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 restart Amavis to take effect:

sudo /etc/init.d/amavis restart




Anomy Configure


Now lets get Anomy installed and running. First we’ll have to download it from their website.

steve @ debian ~ :) ?>   cd ~
steve @ debian ~ :) ?>   wget
HTTP request sent, awaiting response... 200 OK
Length: 172722 (169K) [application/x-gzip]
Saving to: โ€œqc?โ€

100%[================================================================================>] 172,722      168K/s   in 1.0s    

2012-12-27 15:26:38 (168 KB/s) - โ€œqc?โ€ saved [172722/172722]


Now to move it to it’s new home and unpack it. (for some reason the file name wasnt right so we need to rename it)

sudo mv qc\? /usr/local/anomy-sanitizer-1.76.tar.gz
cd /usr/local/
sudo su
tar -zxvf anomy-sanitizer-1.76.tar.gz
cd anomy
ls -alh


For starters on configuration, I found a site that provides a baseline config that we’ll work off of. Thanks to “” for this one! We’ll use this conf file to start with. If that link doesn’t work, here it is on my site: anomy.conf.

Download that file and place it in your /usr/local/anomy/ folder.




Allow Mail to be Scanned: Postfix Configuration


Now what we need to do is setup Postfix to actually send the mail to the Spam Filtering engines. In order to make this happen we’re going to have to modify some postfix files. We’re also going to setup the “client_access”, “helo_access”, “sender_access” and “transport” files. We’ll talk more about that when after we modify the “main” and “master” files for Postfix. Basically, these files further enhance how Postfix is able to start the filtering process before mail even gets to the SPAM Filtering Engines. It is here that we start invoking services such as,,, and that work by notifying servers like our that a domain is either blacklisted or black-holed. PLEASE Visit their sites for more information. Let’s start by looking at the “” file. To look at the “” file in all it’s glory, check this out. All of the descriptions below are accredited to this that page.

**NOTE**: I’m setting up my configuration with the ability to verify user accounts through Active Directory. The reason for this is to allow Postfix to verify that the email address is valid before processing the mail. This is yet another safeguard against SPAM. Why accept mail for an account that doesn’t exist in your domain? Just block it! I’ll also show you how to secure the communications between Postfix and the domain. We’ll talk about this later. I haven’t added this content yet, but I will in the future!**END NOTE**

What I’m going to do is just post my “” file in here and then comment the hell out of it so you understand the reasons for what is in the file. Please take out ALL of my comments before pasting this config into your “” file! If you don’t, you will most definitely have errors at run time!

# This is the banner that will be seen by all systems connecting to our Postfix server.
smtpd_banner = The Erd-Manor-dot-com ESMTP Relay

#Biff is an old legacy thing that isnt needed anymore and can cause performance issue if left on.
biff = no

#We dont want to help anyone out. If you're hosting more than 1 domain, you better leave this off (no).
append_dot_mydomain = no

#This is how much time Postfix will wait before sending a message back to the originating server
#that there is an issue.
delay_warning_time = 4h

#This tells Postfix where to send mail on the next hop. You need this if you have more than 1 domain.
transport_maps = hash:/etc/postfix/transport

#The Internet hostname of this mail system. The default is to use the fully-qualified domain name (FQDN)
#of your MX record.
myhostname =

#The alias databases that are used for local mail delivery. We'll be modifying this later.
alias_maps = hash:/etc/aliases

#This is just where the aliases exist at.
alias_database = hash:/etc/aliases

#For most cases, your /etc/mailname file should contain the "myhostname" value. In this case,
myorigin = /etc/mailname

#What destination domains (and subdomains thereof) this system will relay mail to.
#This can be a file or a list of domains, that, are, comma, separated
relay_domains =,

#The list of domains that are delivered via the $local_transport mail delivery transport. By default
#this is the Postfix local delivery agent which looks up all recipients in /etc/passwd and /etc/aliases.
#The SMTP server validates recipient addresses with $local_recipient_maps and rejects non-existent
#recipients.This can be a file or a list of domains
mydestination =, localhost

#This is usually the primary IP address of your Internal Exchange Server. This value is trumped by "transport_maps"
# so if you have multiple relay servers, you can comment this out like I have.
#relayhost =

# This is just a list of your internal networks. The list of "trusted" remote SMTP clients that have more
#privileges than "strangers". You can also specify "/file/name" or "type:table" patterns.
mynetworks =,

#The maximal size of any local individual mailbox or maildir file, or zero (no limit). In fact, this limits
#the size of any file that is written to upon local delivery, including files written by external commands
#that are executed by the local delivery agent. This limit must not be smaller than the message size limit.
mailbox_size_limit = 0

#The separator between user names and address extensions (user+foo). Basically, the software tries user+foo
#and .forward+foo before trying user and .forward. Just leave it the way it is.
recipient_delimiter = +

#The network interface addresses that this mail system receives mail on. Specify "all" to receive mail on all
#network interfaces (default) and "loopback-only" to receive mail on loopback network interfaces only.
inet_interfaces = all

#After the message is queued, send the entire message to the specified transport:destination. The transport
#name specifies the first field of a mail delivery agent definition in; the syntax of the next-hop
#destination is described in the manual page of the corresponding delivery agent. More information about
#external content filters is in the Postfix FILTER_README file.
content_filter = smtp-amavis:[]:10024

#Enable or disable recipient validation, built-in content filtering, or address mapping. Typically, these
# are specified in as command-line arguments... Specify zero or more of the following options.
#The options override settings and are either implemented by smtpd(8), qmqpd(8), or pickup(8)
#themselves, or they are forwarded to the cleanup server.
#no_address_mappings means that we will disable canonical address mapping, virtual alias map expansion,
#address masquerading, and automatic BCC (blind carbon-copy) recipients. This is typically specified
#BEFORE an external content filter.
receive_override_options = no_address_mappings

#Require that addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed with <>, and that
#those addresses do not contain RFC 822 style comments or phrases. This stops mail from poorly written
#software. By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM and RCPT TO addresses.
strict_rfc821_envelopes = yes

#Reject the request when the HELO or EHLO hostname has no DNS A or MX record. The
#unknown_hostname_reject_code parameter specifies the numerical response code for rejected requests
#(default: 450). This is a strong way to stop many spammers.
unknown_hostname_reject_code = 450

#The numerical Postfix SMTP server response code when a client without valid address <=> name mapping
# is rejected by the reject_unknown_client_hostname restriction. The SMTP server always replies with
#450 when the mapping failed due to a temporary error condition. Do not change this unless you have a
# complete understanding of RFC 5321. Turning this on can cause a lot of false positives, test this out.
### unknown_client_reject_code = 450

#Disable the SMTP VRFY command. This stops some techniques used to harvest email addresses.
disable_vrfy_command = yes

#Wait until the RCPT TO command before evaluating $smtpd_client_restrictions, $smtpd_helo_restrictions
#and $smtpd_sender_restrictions, or wait until the ETRN command before evaluating
#$smtpd_client_restrictions and $smtpd_helo_restrictions. This feature is turned on by default because
#some clients apparently mis-behave when the Postfix SMTP server rejects commands before RCPT TO.The
#default setting has one major benefit: it allows Postfix to log recipient address information when
#rejecting a client name/address or sender address, so that it is possible to find out whose mail is
#being rejected.
smtpd_delay_reject = yes

#Require that a remote SMTP client introduces itself with the HELO or EHLO command before sending the
#MAIL command or other commands that require EHLO negotiation.
smtpd_helo_required = yes

#You need to read this -->
smtpd_client_restrictions =
        check_client_access hash:/etc/postfix/client_access,
#Below are all of the DNS Blacklists that Spam originates from.

# You need to read this -->
smtpd_helo_restrictions =
        check_helo_access hash:/etc/postfix/helo_access,
#        reject_unknown_helo_hostname, #This can cause false positives, test before production!

smtpd_sender_restrictions =
        check_sender_access hash:/etc/postfix/sender_access,
        reject_unknown_sender_domain, #This can cause false positives, test before production!

smtpd_recipient_restrictions =
        reject_non_fqdn_hostname, #This can cause false positives, test before production!

smtpd_error_sleep_time = 1s
smtpd_soft_error_limit = 10
smtpd_hard_error_limit = 20

# Basic SPAM prevention...Require that a remote SMTP client introduces itself with the HELO or
#EHLO command before sending the MAIL command or other commands that require EHLO negotiation.
smtpd_helo_required = yes



Wow, that took forever…



Now we need to jump into the “” file. This one is a bit more tricky than the “” in that it has a lot more little tweaks. For more info on “”, there is an excellent “FAQ” on Postfix’s website: HERE. Here we go, I’ll do this the same as I did for the “” file, attempting to explain as much as I can so that you understand what everything is doing. ๐Ÿ™‚ Remember to take out ALL of my comments before pasting this config into your โ€œmaster.cfโ€ file! If you donโ€™t, you will most definitely have errors at run time!


Here we go, here’s my “” file:

# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
smtp      inet  n       -       -       -       -       smtpd
#submission inet n       -       -       -       -       smtpd
#  -o milter_macro_daemon_name=ORIGINATING
#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       -       -       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_fallback_relay=
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
maildrop  unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${recipient}
uucp      unix  -       n       n       -       -       pipe
  flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)

smtp-amavis     unix    -       -       -       -       2       smtp
        -o smtp_data_done_timeout=1200
        -o smtp_send_xforward_command=yes
        -o disable_dns_lookups=yes
        -o max_use=20 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=
        -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


Now we need to take care of our “client_access”, “helo_access”, “sender_access” and “transport” files as we spoke of earlier. There are many types of these files that can be referenced by the “” file, but these are really the only ones we need. Theoretically, we could have created a bunch more of these, and in a large enterprise that owns hundreds or thousands of domains, it’s almost a necessity to do so. For all the info you need about these files look at the database webpage and the man 5 access page.

Back in the “” file, we added a line item in there that looks like this, “check_client_access hash:/etc/postfix/client_access“. The purpose of the Client Access file is to “search the specified access database for the client hostname, parent domains, client IP address, or networks obtained by stripping least significant octets.” So what does that mean? Basically it means that this file is like access control list for remote SMTP servers. It checks client information: host names, network addresses, and envelope sender or recipient addresses.

As a safeguard, we should NEVER be accepting email from our own domain, from a remote source. Our Exchange server is inside our organization already and will process our internal mail for us. This proxy will deny anyone out on the internet trying to spoof mail into our domain. You want to make sure to have every domain you own in this list. And you can also do some “whitelisting” in here as well. Let’s get our “client_access” file going:        REJECT       REJECT       OK     OK       OK    OK


Now for our “helo_access” file. This file is much the same, it’s another ACL that we are setting up. Postfix states that this command will tell the Postfix server to “Search the specified access database for the MX hosts for the HELO or EHLO hostname, and execute the corresponding action . Note 1: a result of “OK” is not allowed for safety reasons. Instead, use DUNNO in order to exclude specific hosts from blacklists. Note 2: specify “smtpd_helo_required = yes” to fully enforce this restriction (without “smtpd_helo_required = yes”, a client can simply skip check_helo_mx_access by not sending HELO or EHLO).            REJECT           REJECT
/^smtp\.erdman\.cc$/        550 Dont use my own hostname
/^smtp\.erdmanor\.com$/     550 Dont use my own hostname
/^mail\.erdman\.cc$/        550 Dont use my own hostname
/^mail\.erdmanor\.com$/     550 Dont use my own hostname
/^ns1\.erdman\.cc$/     550 Dont use my own hostname
/^ns1\.erdmanor\.com$/      550 Dont use my own hostname
/^ns2\.erdman\.cc$/     550 Dont use my own hostname
/^ns2\.erdmanor\.com$/      550 Dont use my own hostname
/^\[108\.227\.33\.121\]$/   550 Dont use my own IP address
/^\[108\.227\.33\.122\]$/   550 Dont use my own IP address
/^\[108\.227\.33\.123\]$/   550 Dont use my own IP address
/^\[108\.227\.33\.124\]$/   550 Dont use my own IP address
/^\[108\.227\.33\.125\]$/   550 Dont use my own IP address
/^[0-9.]+$/         550 Your software is not RFC 2821 compliant
/^[0-9]+(\.[0-9]+){3}$/     550 Your software is not RFC 2821 compliant


Moving right along here, lets look at the “Sender_Access” file here. Again, this is another ACL that is supposed to search the specified access database for the MAIL FROM address, domain, parent domains, or localpart@, and execute the corresponding action. We want all of our domains in here as well, and for the same reason as the “client_access” file.            REJECT               REJECT    OK       OK


And lastly, our transport file. This file is really important. Without this working properly we wont get any mail at all from this proxy.        smtp:[]       smtp:[]


Now that we have our access and transport files completed, we need to make them usable to Postfix. The only way that’s possible is to run the “Postmap” command on them.

sudo postmap client_access
sudo postmap helo_access
sudo postmap sender_access
sudo postmap transport




Now that Postfix is setup and ready to go, lets get that restarted and watch our log files at the same time. You should still have a second terminal open, so start your “tail” and then you can restart Postfix.

steve @ debian ~ :) ?>sudo tail -f /var/log/syslog
steve @ debian ~ :) แ›ค>   sudo /etc/init.d/postfix restart
Stopping Postfix Mail Transport Agent: postfix.
Starting Postfix Mail Transport Agent: postfix.


Here is the output from the tail:

Dec 28 11:34:12 debian postfix/master[1481]: terminating on signal 15
Dec 28 11:34:12 debian postfix/master[3266]: daemon started -- version 2.7.1, configuration /etc/postfix



At a bare minimum here, assuming your DNS records are setup properly, your MX records have propagated throughout the Internet, your Firewall is setup properly, your Exchange box is setup properly, and the other million variables are good, you should be able to drop this in between your firewall and your Exchange server. I would suggest putting this in a DMZ that is forward facing to the internet as I explained in one of my previous blogs “Serious network architecture that works for everyone“.



SPAM Filter: SpamAssassin Configuration

Now that our Postfix Proxy is moving mail properly, lets get some SPAM engines configured. ๐Ÿ™‚ We’ll start with SpamAssassin. A brief background on SpamAssassin: This product is an open source code set that is actually used in a TON of other SPAM filtering products behind the scenes.

Let’s get a quick idea of where SpamAssassin stores it’s files:




Here is what my “/etc/spamassassin/” file looks like. I’ll comment on the file as I did earlier in this blog. Dont forget to remove ALL “#comments” before using this in your configuration. If you donโ€™t, you will most definitely have errors at run time! Also, according to SpamAssassin, “There are now multiple files read to enable plugins in the /etc/mail/spamassassin directory; previously only one, “init.pre” was read. Now both “init.pre”, “v310.pre”, and any other files ending in “.pre” will be read. As future releases are made, new plugins will be added to new files, named according to the release they’re added in.” So we’re going to have to go through that stuff as well. Again, if you would like any further information regarding this, I urge you to visit the SpamAssassin page for the configuration settings.

# I recommend not using this for this implementation. Our Postfix Server is acting as a Proxy to our
# Exchange server. If you have internal servers that need to get mail to your users, then the best
# place to handle that workload is at the Exchange Server Receive connectors. Send you internal mail there.
# trusted_networks

#Here is where we do our subject line rewrite for mail that is marked as SPAM.
rewrite_header Subject  [***** SPAM _SCORE_ *****]

#Score that a message needs to get to in order to be classified as SPAM.
# this number is actually pretty high, but after tweaking it, you can lower it to 4.5 or 5.0.
required_score      7.0

#If the mail message meets the two above requirements the message is then packed up into an attachment and
# forwarded to the recipient in plain text. It is up to the user to inspect and go from there.
report_safe     2

# Turn on DCC
# dcc
use_dcc 1
dcc_path            /usr/bin/dccproc
dcc_add_header          1
dcc_dccifd_path         /usr/sbin/dccifd

# Turning on the skip_rbl_checks setting will disable the DNSEval plugin, which implements Real-time Block
# List (or: Blackhole List) (RBL) lookups. We WANT Those checks to happen so leave this at ZERO (0).
skip_rbl_checks     0

use_razor2          1
razor_config            /etc/razor/razor-agent.conf

pyzor_options           --homedir /etc/mail/spamassassin discover
use_pyzor           1
pyzor_path          /usr/bin/pyzor
pyzor_add_header        1

# Language and Location options. I have mine set to only allow English. If you work at a large international
# business you'll want to setup all the languages your company communicates in or just say allow all:
#  ok_locales all         (allow all locales)
#  ok_locales en          (only allow English)
#  ok_locales en ja zh    (allow English, Japanese, and Chinese)
ok_locales              en

# The next three deal with the Bayes system and how SpamAssassin actually can "learn" spam.
use_bayes       1
use_bayes_rules     1
bayes_auto_learn    1
use_learner 1

# If you receive mail filtered by upstream mail systems, like a spam-filtering ISP or mailing list, and that
# service adds new headers (as most of them do), these headers may provide inappropriate cues to the Bayesian
# classifier, allowing it to take a "short cut". To avoid this, list the headers using this setting. Example:
# bayes_ignore_header X-Upstream-Spamfilter
# bayes_ignore_header X-Upstream-SomethingElse
bayes_ignore_header X-Bogosity
bayes_ignore_header X-Spam-Flag
bayes_ignore_header X-Spam-Status

# To be accurate, the Bayes system does not activate until a certain number of ham (non-spam) and
# spam have been learned. The default is 200 of each ham and spam, but you can tune these up or
# down with these two settings.
bayes_min_ham_num        20 #default is 200
bayes_min_spam_num       20 #default is 200

# The Bayes system will, by default, learn any reported messages (spamassassin -r) as spam.
# If you do not want this to happen, set this option to 0.
bayes_learn_during_report      1

# SpamAssassin will opportunistically sync the journal and the database. It will do so once a day,
# but will sync more often if the journal file size goes above this setting, in bytes. If set to
# 0, opportunistic syncing will not occur.
bayes_journal_max_size        102400

# What should be the maximum size of the Bayes tokens database? When expiry occurs, the Bayes
# system will keep either 75% of the maximum value, or 100,000 tokens, whichever has a larger
# value. 150,000 tokens is roughly equivalent to a 8Mb database file.
bayes_expiry_max_db_size      200000

# If enabled, the Bayes system will try to automatically expire old tokens from the database.
# Auto-expiry occurs when the number of tokens in the database surpasses the
# bayes_expiry_max_db_size value.
bayes_auto_expire      1

# If this option is set, whenever SpamAssassin does Bayes learning, it will put the information
# into the journal instead of directly into the database. This lowers contention for locking the
# database to execute an update, but will also cause more access to the journal and cause a delay
# before the updates are actually committed to the Bayes database.
bayes_learn_to_journal (default: 0)

#   Some shortcircuiting, if the plugin is enabled
ifplugin Mail::SpamAssassin::Plugin::Shortcircuit

#   default: strongly-whitelisted mails are *really* whitelisted now, if the
#   shortcircuiting plugin is active, causing early exit to save CPU load.
#   Uncomment to turn this on
shortcircuit USER_IN_WHITELIST       on
shortcircuit USER_IN_DEF_WHITELIST   on
shortcircuit USER_IN_ALL_SPAM_TO     on
shortcircuit SUBJECT_IN_WHITELIST    on

#   the opposite; blacklisted mails can also save CPU
shortcircuit USER_IN_BLACKLIST       on
shortcircuit USER_IN_BLACKLIST_TO    on
shortcircuit SUBJECT_IN_BLACKLIST    on

#   and a well-trained bayes DB can save running rules, too
shortcircuit BAYES_99                spam
shortcircuit BAYES_00                ham

endif # Mail::SpamAssassin::Plugin::Shortcircuit



Here’s that Exact same file without all the comments:

rewrite_header Subject  [***** SPAM _SCORE_ *****]
required_score          7.0
report_safe         2
use_dcc 1
dcc_path                /usr/bin/dccproc
dcc_add_header          1
dcc_dccifd_path         /usr/sbin/dccifd
skip_rbl_checks     0
use_razor2          1
razor_config            /etc/razor/razor-agent.conf
pyzor_options           --homedir /etc/mail/spamassassin discover
use_pyzor               1
pyzor_path          /usr/bin/pyzor
pyzor_add_header        1
ok_locales              en
use_bayes       1
use_bayes_rules     1
bayes_auto_learn    1
use_learner 1
bayes_ignore_header X-Bogosity
bayes_ignore_header X-Spam-Flag
bayes_ignore_header X-Spam-Status
bayes_min_ham_num        20 #default is 200
bayes_min_spam_num       20 #default is 200
bayes_learn_during_report      1
bayes_journal_max_size        102400
bayes_expiry_max_db_size      200000
bayes_auto_expire      1
bayes_learn_to_journal (default: 0)

ifplugin Mail::SpamAssassin::Plugin::Shortcircuit

shortcircuit USER_IN_WHITELIST       on
shortcircuit USER_IN_DEF_WHITELIST   on
shortcircuit USER_IN_ALL_SPAM_TO     on
shortcircuit SUBJECT_IN_WHITELIST    on

shortcircuit USER_IN_BLACKLIST       on
shortcircuit USER_IN_BLACKLIST_TO    on
shortcircuit SUBJECT_IN_BLACKLIST    on

shortcircuit BAYES_99                spam
shortcircuit BAYES_00                ham

endif # Mail::SpamAssassin::Plugin::Shortcircuit


Now we need to restart SpamAssassin and test out our changes.

sudo sa-update -D --updatedir /tmp/updates
sudo /etc/init.d/spamassassin restart
echo "test" | sudo spamassassin -D pyzor 2>&1 | less


Alright, enough SpamAssassin stuff. Let’s get Amavis up and running.



SPAM Filter: Amavis-New Configuration

Now that our Postfix Proxy is moving mail properly, and SpamAssassin is filtering mail, lets get some Amavis-New configured. Remember what we said before: Amavis sends mail to SpamAssassin by default. That is the reason why we setup SpamAssassin first. In order to have Amavis properly scanning mail we’ll be configuring files in your /etc/amavis/ directory. Before we jump into that, lets get an Idea of where Amavis is located in your Server. Below is where Amavis has files by a default install:



I know that seems like a lot, but we’ll try cover it all. Amavis is really a different beast than SpamAssassin. But since SpamAssassin is already doing the brunt force of the work, we can take our time in this one a bit.






SPF Records

The last thing I wanted to cover in this blog, since we’re hosting our own DNS and Mail servers, it would only be right for us to cover DNS SPF records. This is just another layer of security that we *should be* using to help strengthen, not only our email, but our whole external domain.




I updated this again on 2/3/13. But I’m lazy, so… there’s no change log. ๐Ÿ™‚



References for this blog go out to:

VN:F [1.9.22_1171]
Rating: 5.0/5 (1 vote cast)
VN:F [1.9.22_1171]
Rating: 0 (from 0 votes)