Author: Anders Berggren

Why everybody should use DMARC to prevent phishing

Email is a major source of phishing and malware attacks. The Locky ransomware solely contributed to a 412% increase of malware emails in March compared to February, according to CYREN’s May 2016 cyberthreat report. While I believe that awareness and training is the most universally effective counter-measure, even that is really difficult, according to this recent study. We probably need a combination of training and technological advancements. One of the latter has to do with email authenticity. Can you trust an email’s sender adress? Generally no, but you can with DMARC. Read more.

Traveling from Ace to Monaco (editor)

Microsoft revealed a project called “Monaco” in November 2013 as a part of the online version of Visual Studio. A few years later, the open source Visual Studio Code editor was released, which also used it as foundation. Finally, in June 2016, Microsoft released a standalone version of the Monaco Editor on GitHub.

Amazed by its snappiness and the look ‘n feel of its diff utility, we added it to our script language‘s IDE right away, publishing a sneak peek complete with IntelliSense code completion just a few days later. You can check it out on our demo system.

We’re very happy to announce that the Monaco integration is part of our Halon 3.5-r3 release that we shipped in early August (2016). The Ace editor (by Cloud9) have served us very well during many years, and remains an important part of our product as it continues to be used in for example the “flow chart” block’s scripting area.

Finally we like to thank Alexandru Dima and everybody else who has been working on Monaco for this excellent piece of software. Read more.

Using reCAPTCHA to handle spam misclassification

Today’s leading spam filter technologies offer a very high degree of accuracy. In this blog I’ll describe the current state of spam classification, and propose a pretty innovative method that can significantly improve both senders’ and recipients’ satisfaction (as well as reducing the burden on administrators and support staff) by enabling senders to report false positives if they pass a CAPTCHA test. Let’s start by familiarising ourselves with the history of anti-spam.

Read more.

What’s new in Halon 3.5 “sunny”

Spring is here, and so is the 3.5 release (codename sunny) of the Halon SMTP software! It includes major features such as an IDE-style script editor and object orientation, is based on FreeBSD 10.3 and comes with the latest quarterly packages. In other words, this release marks another milestone for Halon’s developer friendliness.

Read more.

What Gmail’s new TLS icon really means

Google’s recent announcement that they’ll be adding encryption (TLS) and authentication (DKIM/DMARC) status icons to Gmail is a great initiative.

What they do

In addition to being displayed for received email, the encryption indicator works when composing email as well. It’s however not updated in realtime, and seems to be cached per domain. For example, a warning is displayed “”, but not for “”, despite pointing to the same MX. We haven’t been able to verify how long it takes for the warning to display; after setting up a new (non-TLS) domain one day ago and sending numerous email to it from different Gmail accounts, the warning is nowhere to be seen. We presume that the sessions of sent email are being used is material, since we didn’t record any additional probes/callouts to our test server.

I fully appreciate Google’s rationale behind displaying a red broken lock icon when TLS is absent, rather than a green lock when it is used; I just wished they addressed the shortcomings of non-authenticated TLS and took a stance on how we could move on to proper email encryption.

The problem

As I discussed in a recent blog, TLS is widely deployed for email, but virtually no-one is doing verification (checking authenticity). In the case of a web browser, TLS without verification triggers a warning (such as a red lock). It might be confusing for users that a similar symbol in Gmail indicates something different. In my opinion, there should have been at least an explaination or comment that non-authenticated (opportunistic) TLS doesn’t protect against active attacks (eavesdropping, downgrade, etc).

The main issue, of course, is that there’s currently no widely deployed mechanism for SMTP TLS name verification. This stems from the fact that email is security-agnostic (unlike the web, where you type “https://”) and that the DNS MX structure makes normal CA-based name verification ambiguous.

What they could do

The most promising technology right now for proper, verified encryption (TLS) is probably DANE, which builds on DNSSEC. It’s already implemented in Postfix (the second most popular email server) and (of course) Halon. Furthermore, many European providers and operators have either deployed, or is planning to deploy, DANE. It even serves as a cornerstone for Trusted Email Services initiative.

While its dependency on DNSSEC is likely hampering adoption, I’m encouraged by its strong community support. It feels like widespread email encryption is finally within reach!

What is DANE?

DANE does not only challenge the certificate authority (CA) system, but also has the potential to revolutionize email security; namely making encrypted email delivery the norm. Halon Security’s mission is to bring DANE to the world of email and to help maintain data privacy and security on a global scale.

The DNS-based Authentication of Named Entities (DANE) is a proposed standard that binds X.509 certificates to DNS names using Domain Name System Security Extensions (DNSSEC).

Even today (2016), email is being transmitted unencrypted, with very few exceptions. The fact that many servers use TLS doesn’t do much more than create a false sense of security; while it prevents passive wiretapping, the opportunistic TLS mode that is being used today doesn’t protect your email transmissions from active attacks. DANE is currently the most promising piece of technology that might change all that. Despite being (primarily) a DNSSEC-based trust scheme for X.509 certificates, it also provides the means to know if a domain supports encrypted email transfer. That last part is very important; it’s what has been missing all these years.


Public-key cryptography is a fundamental component that makes the modern Internet work the way it does. One of the most widely known encryption protocols is TLS (formerly SSL), used for web browsing, instant messaging, and much more.

Email however, despite being “the go-to form of communication in the Business world” with a constantly growing user base, hasn’t changed much over the years, and is generally not encrypted.

The state of email encryption

Before we start talking about DANE, let’s first look at the differences between transport and end-to-end encryption;

  • Transport encryption works on domain level (an organization) and protects the email transfer. It is similar to HTTPS, used when browsing secure websites.
  • End-to-end encryption works on the individual level (a person) and protects the content of the email for its entire lifetime. The two most popular standards are S/MIME and PGP, but none of them have achieved widespread adoption.

While I would certainly love to see widely deployed end-to-end email encryption in the future, having transport security in place would be a very good start. When visiting your bank’s website, it’s surely encrypted. Still, when sending them an email, the transport from your email server to theirs, likely isn’t. Why is that? Since email transfer (SMTP) supports TLS, why not use a PKI such as the CA system, like we do for the web? Unfortunately, there’s no standard defining a way for the sending server to know whether to use encryption or not. For the web, you type https://, and there’s simply no equivalent for email. Until DANE.

Introducing DANE

DANE is proposed in RFC 6698 by Hoffman and Schlyter as an alternative to CAs. The CA system has been subject to criticism during the last years, following compromise and mishaps of several major CAs. To make things worse, the revocation systems doesn’t work very well in practice. DANE builds on DNSSEC which provides a hierarchal scheme (the root, TLDs, domains and so on), as opposed to the flat CA system where any trusted CA can issue a certificate in the name of anyone.

Is the general consensus that DANE should replace CAs all together? As always there are arguments for and against. While a hierarchal system is preferable, the transfer of control and responsibility to the DNS system’s owners (governments, DNS admins) is a topic much discussion. There’s also work to improve the CA system with supplementary techniques such as key pinning and added perspective. Nevertheless, DANE stands strong to improve the security in many areas, such as email.

DANE for email

Postfix was probably the first email server to support RFC 7672 (DANE for SMTP), and Exim support is underway. The fact that those two are the most widely used SMTP servers, and the somewhat strong DNSSEC adoption, is a solid foundation for DANE. Halon’s MTA supports DANE since 3.4-rocky-r2.

Start using DANE

Most of our customers can start sending email with DANE right away, by simply changing TLS mode to dane. We recommend that you use the built-in DNS resolver Unbound with DNSSEC enabled, instead of relying on an external DNS server’s AD-bit. In the logs you can identify DANE-verified connections by

Connecting to [2001:1900:2254:206a::19:1]:25 (DNSSEC)
X.509: /OU=Domain Control Validated/OU=Gandi Standard SSL/ issued by…
DANE: validated successfully
Connection is now using TLS

If you or your customers’ domains are DNSSEC signed, you should look into receiving email with DANE as well. In theory, it’s no more difficult than publishing your SMTP servers’ certificate signatures as TLSA records in your DNS using the same name as the MX points at, but prefixed with _25._tcp, for example: IN A IN TLSA 3 0 1 2B73BB905F…

Enter Halon

We have been pioneering email security in our scriptable SMTP server for a long time; being early adopters of DMARC, DNSSEC and much more. If you’re curious, go ahead and download the software from our website.

More elegant Halon scripting with lambda abstraction

At the center of the Halon SMTP platform is our domain-specific scripting language. As our users are well aware, the syntax is inspired by languages such as PHP (e.g. $variable) and Python (e.g. slices [0:10]). Although the implementation differs vastly, the concept of having a purpose-tailored scripting language as a form of configuration exists in other projects as well, such as Varnish.

In our pursuit of even more readable and elegant solutions, we’ve extended the scripting language to support various aspects of lambda abstraction; namely

Making functions first-class citizens makes a lot of sense, given that most of our customers already uses callbacks functions for things like external API calls’ cache behaviour.

Although HSL is arguably very similar to PHP, keep in mind that they are different languages with different syntax. Unlike PHP, all array_ functions takes the callback function as the first argument.

$strings = array_filter(is_string, $array);
$double = array_map(function ($x) { return $x*2; }, $array);

You’ll likely see more of anonymous functions in the future; this is just the beginning!

End-user improvements and new integrations with cPanel and Odin

Although many customers prefer to use the Halon SMTP Platform as-is, most hosting providers want to implement end-user interfaces in order to offer a higher degree of customer self-service. Since the Halon SMTP platform is essentially a scriptable MTA (with many features such as anti-spam, signing, and much more) with an open source ecosystem, it makes a lot of sense to maintain the end-user interface as a GitHub project. It is designed as a boiler-plate, and our aim is that the code itself should be as simple and straight-forward as possible. It currently offers features such as indexed history, text logs, queue and quarantine management, black/whitelisting, spam settings and statistics.

In the previous weeks, we’ve added translation support using gettext, with English as the default language, and an extra translation in Swedish. If you want to maintain a translation in another language; please let us know! The language is automatically detected based on the browser’s HTTP_ACCEPT_LANGUAGE.

Rebranding is also made easier thanks to templates written in Smarty, which is also used for email notifications.

One of Halon’s strengths is seamless integration, something that we discussed in the previous blog entry. The same goes for the end-user interface, and we’ve done numerous integrations with common hosting platforms such as WHMCS, cPanel and Odin. The cPanel plugin is branched out into its own project, and offers session transfer for both admins and users (webmail). We recently went to Barcelona for an APS2 training hosted by Odin, and we’ve published an initial version of our Service Automation plugin. It currently offers session transfer for both admins and users, and we’re looking to extend its functionality in various ways.

We hope that you and your customers will enjoy the updated end-user experience! Do not hesitate to contact us if you want more information or help setting it up.

Seamless integration with external APIs using Halon scripting

The Halon SMTP platform is unique in its scriptable approach to email. For those of you who still haven’t discovered the tangible business benefits of the tight integrations that this allows for, we’d like to showcase this in the video demonstration below. It surely is key to improving and streamlining your current email infrastructure.

Unlike most other anti-spam and email gateways, there’s no need to add domains and users to the Halon system. Our scriptable approach to SMTP makes it possible to avoid information duplication (which inevitably becomes out of sync) by querying (and dynamically caching) external sources. While similar to the “LDAP recipient lookup” that many email gateways support, the Halon scripting language takes you light-years further than that. Just take a look at our REST API call example that employs both short- and long-term caching and execution-time rate limits to create an incredibly robust method for external lookups via HTTP/JSON.

Fredrik has created a video that introduces those concepts, so that you can get a better apprehension for how they work seamlessly together!

Our customers use such scripts to implement dynamic routing, per-domain DKIM signing, automatic reporting and blocking of abusive users to end-user systems and much more, in order to perfectly integrate with their surrounding environment.

New Halon 3.4 “rocky” release

We’re very proud to announce the 3.4 release (codename rocky) of the Halon email gateway software! It’s based on FreeBSD 10.2 and comes with updates to virtually all components of the system; the CYREN anti-spam engines (now implemented using ctasd), OpenSSL, and many more.

Being a major release, it also comes with hundreds of new, small features. For example, it adds a SetTLS function to the pre-delivery script (yet another way of handling mail servers with broken SSL implementations), a pie chart function called q() that can be used to visualize the queue and quarantine, and zoomable line graphs on the statistics page which layout can be saved per user.

As a result of the news features in the email gateway, our logging and end-user interface has been updated to take advantage of those improvements as well. On another note, we’ve released an updated version of our cPanel plugin as a stand-alone package which adds support for the paper lantern skin.

As usual, new systems are deployed by downloading a disk image or virtual machine template, and running systems updated by simply pressing the automatic update button on the web admin’s update page.