Debian, Qmail, SMTP

Plugging QPSMTPD Service With QMAIL

QPSMTPD is a flexible smtp daemon written in Perl. Apart from the core SMTP features, all functionality is implemented in small extension plugins using the easy to use object oriented plugin API. Basically I uses Qmail Based mail server’s with a custom qmailqueue. We uses the tcpsvd (TCP/IP Service Daemon) for the smtp service and the mails are passed to a custom qmailqueue which is basically a perl script with custom filters for filtering out the mails. QPSMTPD has a verity of custom plugins which includes SPF check, DKIM check and even for DMARC also. If you are a Perl guy, then you can build custom plugins. The main reason why i got attracted to QPSMTPD was because of its plugin nature.

In this blog i will explain on how to setup QPSMTPD along with QMAIL MTA. As i mentioned earlier, i’m using a custom qmailqueue, where i have some custom filtering which varies from client to client. So i will be using QPSMTPD to do initail filtering like checking DNSBL/RBL, SPF check, DKIM, DMARC etc. A breif info about various qpsmtpd plugins are available here

Ths qpsmtpd source is available in Github. The soucre comes with default run scripts which can be used with runit/daemontools. Clone the qpsmtpd source and install the dependency Perl modules.

$ git clone https://github.com/smtpd/qpsmtpd/

$ cpan -i Net::DNS

$ cpan -i MIME::Base64

$ cpan -i Mail::Header

Now create a user for the qpsmtp service, say ”smtp” with home folder as the location of the qpsmtpd folder and chown the qpsmtpd folder using the smptp user. Add sticky bit to the qpsmtpd folder by running chmod o+t qpsmtpd, in order to make supervise start the log process. By deafult inside the source folder there will be a sample config folder called “config.sample”. Copy the entire folder and create a new config folder.

$ cp config.sample config

In the config folder, edit the ”IP” in order to mention which ip the qpsmtpd daemon should bind. Putting “0” will bind to all the interfaces. Now if we go through the qpsmtpd’s run script in the source folder, it depends on two binaries softlimit and tcpserver. The softlimit binary comes with the daemontools debian package and the tcpserver binary comes with the ucspi-tcp debian package. so let’s install those two packages.

$ apt-get install ucspi-tcp daemontools runit

Now start the qpsmtpd server. I’m using runit for service supervision.

$ update-service --add /usr/local/src/qpsmtpd qpsmtpd

The above command will add the service. We can check the service status using sv s qpsmtpd command. This will show us whether the serivce is running or not. Now go inside the “config” folder and open the “plugin” file. This is where we enable the plugins, by addin the plugin names with corresponding options. By default the ”rcpt_ok” plugin must be enabled. This plugin handles the qmail’s rcpthosts feature. It accepts the emails for the domains mentioned in the ”rcpthosts” file present in the config folder. If this is not enabled it will not accept any mails. So the best way to understand how each plugin works is comment out all the plugins except “rcpt_ok” and then add the plugins one by one. The plugins are available in the “plugin” folder in the qpsmtpd source folder. All the basic info about the plugins are mentioned in the plugin files itself.

Now most commonly used plugins are auth for SMTP AUTH, DNSBL/RBL, spamassassin, etc. We can enable these plugins by adding the names in the config/plugin files. For example, since i’m using a custom qmailqueue, once the qpsmtpd has accepted the mail, it has to be queued to my custom QMAILQUEUE. So i need to enable the “queue plugin”. I can enable the plugin by adding the below line to the plugin file inside the config folder.

queue/qmail-queue /var/qmail/bin/qmail-scanner-queue

If you are using any other MTA, you can provide the corresponding MTA’s queue. For example for postfix ”postfix-queue”, and for exim use ”exim-bsmtp”, or if you want to use QPSMTPD as a relaying server, you can use ”smtp-forward” plugin for relaying mails to another SMTP server. So once the mail has been accepted by qpsmtpd, it will queue the mail to my custom qmail queue, and then it will start the mail delivery. Similarly i use ldap backend for smtp authentication. So i need to enable ”auth/auth_ldap_bind” plugin for this. Like that we can add other plugins too. By default DMARC plugin is not added, but we can get it from here.

Use tools like swaks for sending test mails, because plugins like check_basicheaders will not accept mails without proper headers, so using telnet to send mails wont work some times. Swaks is a good tool for sending test mail. We can increase the loglevel, by editing config/loglevel file. It’s better to increase the log level to debug so that we will get more details of errors. Some plugins needs certain Perl modules, if it’s missing the error will popup in the qpsmtpd logs, so use cpan and install those perl modules.

By default the run script uses tcpserver to start the service. There many other ways of deployments like forkserver,pre-fork daemon,Apache::Qpsmtpd etc. To use the default TLS plugin, we need to use the ”forkserver model”. The forke server model script is availbale in the same run script, but it is commented by default. The default spool directory will be a ”tmp” folder inside the QPUSER’s ie, the user “smtp” home folder. In my case i’m using a separate folder for spool, /var/spool/qpsmtp, for such cases, edit lib/Qpsmtpd.pm and go to ”spool_dir” subroutine and add ”$Spool_dir = “/var/spool/qpsmtpd/”;”. Now create the spool directory with owner as ”smtp” user and folder permission ”0700” and then restart the qpsmtpd service.

Now to enable TLS, enable the tls plugin in the config/plugin file like this ”tls cert_path priv_key_path ca_path”. If there is no TLS certificate available ,then we can generate using a perl script ”tls_cert”, which is available at the plugins folder. Now we need to edit the config/tls_before_auth file and put the value “0”, otherwise AUTH will not be offered unless TLS/SSL are in place. Now we can try sending a test mail using swaks with TLS enabled. Below is my swaks output.

=== Trying 192.168.42.189:587...
=== Connected to 192.168.42.189.
<-  220 beingasysadmin.com ESMTP  send us your mail, but not your spam.
 -> EHLO deeptest.beingasysadmin.com
<-  250-beingasysadmin.com Hi deeptest [192.168.42.184]
<-  250-PIPELINING
<-  250-8BITMIME
<-  250-SIZE 5242880
<-  250-STARTTLS
<-  250 AUTH PLAIN LOGIN CRAM-MD5
 -> STARTTLS
<-  220 Go ahead with TLS
=== TLS started w/ cipher xxxxxx-xxx-xxxxxx
=== TLS peer subject DN="/C=XY/ST=unknown/L=unknown/O=QSMTPD/OU=Server/CN=debwheez.beingasysadmin.com/emailAddress=postmaster@debwheez.beingasysadmin.com"
 ~> EHLO deeptest.beingasysadmin.com
<~  250-beingasysadmin.com Hi deeptest [192.168.42.184]
<~  250-PIPELINING
<~  250-8BITMIME
<~  250-SIZE 5242880
<~  250 AUTH PLAIN LOGIN CRAM-MD5
 ~> AUTH PLAIN AGRlZXBhawBteWRlZXByb290
<~  235 PLAIN authentication successful for deepak - authldap/plain
 ~> MAIL FROM:<deepak@beingasysadmin.com>
<~  250 <deepak@beingasysadmin.com>, sender OK - how exciting to get mail from you!
 ~> RCPT TO:<deepakmdass88@gmail.com>
<~  250 <deepakmdass88@gmail.com>, recipient ok
 ~> DATA
<~  354 go ahead
 ~> Date: Wed, 01 May 2013 23:19:54 +0530
 ~> To: deepakmdass88@gmail.com
 ~> From: deepak@beingasysadmin.com
 ~> Subject: testing TLS + Auth in qpsmtpd
 ~> X-Mailer: swaks v20120320.0 jetmore.org/john/code/swaks/
 ~>
 ~> This is a test mailing
 ~>
 ~> .
<~  250 Queued! 1367430597 qp 9222 <>
 ~> QUIT
<~  221 beingasysadmin.com closing connection. Have a wonderful day.
=== Connection closed with remote host. 
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Debian, DKIM, Qmail

DKIM signing in Qmail

DKIM and SPF are becoming most commonly adopted methods for email validation. Even if we want to use the DMARC (Domain-based Message Authentication, Reporting & Conformance), we need to configure SPF and DKIM first. DMARC acts as a layer above the SPF and DKIM. DMARC allows the receiever’s mail server to check if the Email is aligned properly as per the DMARC policy, and it queries the sender’s DNS server for the DMARC action, ie, whether to reject or quarantine if alignment fails. The action will be mentioned in the TXT record on the Sender’s DNS server. There is a good collection of DMARC training videos available in MAAWG site. We will get a clear idea on how DMARC works from those videos.

In this post, i will explain on how to make Qmail to do DKIM sign on the outgoing mails. There is a qmail-patch method available, but since i’m using qmail-1.0.3 with custom patch, i was not able to use the DKIM patch along with my custom patch. So the next method is to use a wrapper around “qmail-remote”, since qmail-remote is responsible for delivering remote mails, a wrapper around it will help us to sign the email and then start the remote delivery. There are a few wrappers mentioned in this site. I’m going to use this qmail-remote wrapper.

Initial Settings

First move the current ”qmail-remote” binary to ”qmail-remote.orig”. Now download the wrapper and move it to the /var/qmail/bin/ file.

$ mv /var/qmail/bin/qmail-remote /var/qmail/bin/qmail-remote.orig

$ wget -O /var/qmail/bin/qmail-remote "http://www.memoryhole.net/qmail/qmail-remote.sh"

$ chmod 755 /var/qmail/bin/qmail-remote

This wrapper depends on two programs, 1) dktest, which comes with the libdomainkeys, 2) dkimsign.pl, which is perl script for signing the emails. Both these files, must be available at the path mentioned in the “qmail-remote” wrapper file.

Go through the ”dkimsign.pl” script and install the Perl modules mentioned in it using cpan. There is no official debian package for libdomainkeys, so we need to compile it from the source.

setting up dktest

Download the latest source code from the sourceforge link.

$ tar -xzf libdomainkeys-0.69.tar.gz

$ cd libdomainkeys-0.69

Edit the Makefile and add ”-lresolv” to the end of the ”LIBS” line and run make

$ install -m 644 libdomainkeys.a /usr/local/lib

$ install -m 644 domainkeys.h dktrace.h /usr/local/include

$ install -m 755 dknewkey /usr/bin

$ install -m 755 dktest /usr/local/bin

Generate Domain keys for the domains

Before we can sign an email, we must create at least one public/private key pair. I’m going to create a key pair for the domain “example.com”.

$ mkdir -p /etc/domainkeys/example.com

$ cd /etc/domainkeys/example.com

$ dknewkey default 1024 > default.pub

$ chown -R root:root /etc/domainkeys

$ chmod 640 /etc/domainkeys/example.com/default

$ chown root:qmail /etc/domainkeys/example.com/default

It is very important that the default file be readable only by root and the group which qmailr (the qmail-remote user) belongs to. Now add a TXT entry to the DNS for ”default._domainkey.example.com” containing the quoted part in the /etc/domainkeys/example.com/default.pub

Once everything is added, restart the “qmail-send” and send a test mail to any non local domain. IF things goes fine, we can see a line like the below in “qmail-send” log.

$ @40000000517f518b1e1eb75c delivery 1: success: ktest_---_/tmp/dk2.sign.Gajw948FX1A1L0hugfQ/in_dkimsignpl_---_/tmp/dk2.sign.Gajw948FX1A1L0hugfQ/r74.125.25.27_accepted_message./Remote_host_said:_250_2.0.0_OK_1367298812_ps11si19566038pab.170_-_gsmtp/

Once the DKIM is working properly, add the SPF entries in our DNS, and we are ready to try out DMARC. DMARC is already in use by mail giants like Google,Yahoo,Paypal,Linkedin etc.

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