Halon 5.5 with DSN extension support

Winter is here, and so is our next quarterly Halon MTA release: 5.5 codename “mappy”. It’s slang for happy on a Monday, which is quite fitting! It comes packed with new features, functions and improvements which opens up even greater possibilities for building differentiated, efficient services.

Our large-scale senders will appreciate additional tools for IP warmup, ensuring deliverability by complying with receiver guidelines. You can now choose the order by which source IPs in a pool are chosen, as opposed to load balancing between all IPs. It allows you to use one IP primarily until it exceeds the threshold for daily warmup for a certain destination. Another feature which is especially useful for senders looking at migrating their email infrastructure to cloud environments (such as AWS) is outbound PROXY support. It enables you to use the powerful HAProxy load balancer rather than NAT, when sharing IPs between MTA instances.

Do you want to leverage the DSN extension to better track email delivery? If so, you’ll appreciate our fully-scriptable RFC 3461 implementation. It allows you to quickly and easily tailor the DSN behaviour exactly to your liking.

The Halon scripting language has been extended with new data storage classes, generator functions with yield, and several new functions for encoding. The strongly-typed Map() and Set() storage classes are performance-optimised alternatives to the more generic array type. Take our revamped DMARC implementation‘s public suffix list lookup for example. It parses a data file, then storing and caching the results in a Set() for efficient lookup of the slightly complex rules:

$rules = memory_fetch("public_suffix_list.dat", function ($k) {
		$rules = Set("string");
		$file = File("file://public_suffix_list.dat");
		if (!$file)
			return false;
		while (is_string($line = $file->readline()))
			$line = str_strip($line);
			if ($line[0] == "/" or $line == "")
		memory_store("public_suffix_list.dat", $rules);
			return $rules;

The integrated (VM) package has received several requested features. First of all, the built-in web server which hosts the web administration and JSON API can now be used to also host custom PHP scripts. It allows you to create additional API endpoints, which can write files used by the Halon script during email processing. One possible use case for this is to receive requests from legal interception systems. Secondly, it is now possible to add local DNS records to the built-in Unbound DNS resolver from the web administration. It can be useful when split-horizon DNS is unavailable, and you need to override some specific DNS record. Finally, it allows you to sort the built-in history on both finished and received time. As usual, the package is based on the latest version of FreeBSD (12.2, which was released a few weeks ago) and comes with updated third-party components.

We hope that you will enjoy this new quarterly release. Please see the release notes for more information, and don’t hesitate to reach out if you have any questions!

Are you operating email services?