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Zero disruption, 40% less time managing email: How Rule modernized with Halon

Rule, a Stockholm-based MarTech SaaS platform, relied on PowerMTA for over a decade to power one of its most business-critical operations. But as its needs evolved, so did the risks of relying on legacy infrastructure. Discover how Rule moved to Halon, simplified its email operations, and gained greater flexibility and control all without disrupting its customers.

Key Results

0
Number of customers that faced disruptions
70
% faster implementation of delivery policies
40
% Less time spent managing email infrastructure
50
% Faster identification and resolution of delivery issues

About Rule


Founded in 2007, Rule is a marketing automation platform serving over 3,700 customers, primarily across Europe. Email, SMS, and RCS account for 99% of its communication channels, with email at the heart of the customer journeys it drives.

Part of Rule’s promise is that customers never have to think about deliverability, or how a message renders in Outlook or Gmail. And, as a European company competing predominantly with US platforms, Rule treats GDPR compliance as a competitive advantage, not a checkbox.

The challenge
Rule's most critical system would work until it didn't. And that day was coming.


For around a decade, Rule relied on PowerMTA for its email delivery. It was dependable and familiar, but then the ground started to shift. Repeated ownership changes and its latest owner competing in the same space as Rule raised warning signs about the platform’s long-term viability as a neutral vendor. PowerMTA hadn’t failed. But for a company whose core promise is delivery, relying on it with no plan B became a risk.

Our promise is to deliver messages to the world. PowerMTA will do that, but for us it was a platform that would work until it didn't. Not having a contingency plan was too big a risk.

Sam panel

Sam Jahanfar, CEO, Rule

The day-to-day operational cost was real too. Ten years of configuration had grown into a complex setup of IP pools and configurations (VirtualMTAs). To manage different sending speeds in its existing PowerMTA configuration, Rule maintained multiple versions of the same pools. Its “good” tier alone had grown to 80 VirtualMTAs. IP warm-up never ran on its own, so Sam checked in every day and rerouted traffic by hand whenever a mailbox provider like Yahoo blocked a range.

"As a CEO, I'd say it's suboptimal to have the CEO handling the IPs."

Still, switching was a big call. Email is the most important piece of software at Rule, and the best possible outcome of a migration is that nobody notices. As Sam put it, the upside looked low, and the downside looked steep. Rule needed a partner it could trust with the move.

The solution


Rule evaluated the alternatives on the market and chose Halon for its combination of technical fit, operational flexibility, and support. When evaluating other PowerMTA alternatives, Halon excelled not only in technical capabilities but also in the level of support provided from the very start, which was a major part of the decision.

Rule was replacing infrastructure that already worked, so the migration needed to be handled carefully. The team behind Halon invested significant time during both the evaluation and the transition, including direct involvement from its technical team. Sam describes the experience as “white glove treatment” and says Rule felt prioritized throughout the process, despite not being one of Halon’s largest customers.

Since getting emails out is our main priority, it's really nice to know you can lean on Halon 24/7, 365 days a year. That gives me a lot of confidence that our business is in a stable place.

Sam panel

Sam Jahanfar, CEO, Rule

Protecting Rule's GDPR advantage


Rule competes mainly with US platforms, and its commitment to GDPR compliance is an important competitive advantage. Maintaining control over where customer data is processed and stored is central to that position.

Halon runs on Rule's own servers in the EU, giving the company direct control over its email infrastructure and data residency. Halon's technical team worked alongside Rule's developers to configure the environment around Rule's data protection and operational requirements. Today it runs as a standard, everyday part of Rule's stack.

"Getting that up and running was a real pain point. We could never have pulled it off ourselves. Thanks to the support from the Halon team, it went super smooth."

A migration on Rule's terms


Rather than recreate a decade of PowerMTA configuration, Halon worked with Rule to identify what was still needed and eliminate legacy workarounds. This included simplifying complex IP pool configurations and replacing manual IP warm-up with automated schedules that gradually increase sending volumes. That process left Rule with a much leaner setup and made day-to-day work easier for its DevOps team.

Moving to Halon was as simple as a push of a button. The hard part was shutting down PowerMTA, because there's so much ‘spaghetti’ going on over there. Plus, we had the security of knowing that if PowerMTA did shut down, we could just flip everything over to Halon. So we could take the time we felt we needed. It was a seamless move and was overall very easy to migrate from PowerMTA to Halon.

Sam panel

Sam Jahanfar, CEO, Rule

Results
A seamless migration with zero customer disruption


Rule chose a gradual migration rather than a single cutover, moving traffic stream by stream and IP by IP, at its own pace. The team started with a single low-reputation sender, making it easier to distinguish any existing deliverability issues from problems caused by the new platform.

To maintain IP continuity, Halon routed traffic through HAProxy on Rule's existing PowerMTA server using the PROXY protocol. This allowed both platforms to use the same established sending IPs during the transition, preserving their existing reputation and avoiding the need to warm up new IPs. The migration took a couple of months, but the timeline was driven more by Rule's comfort level than by technical limitations. Sam described moving traffic to Halon as straightforward.

“Looking back, the biggest surprise was how manageable the project had been. Customers saw no disruptions or downtime during the switch, which is the best result a migration can have. Honestly, we should have done this a year ago.”

40% less time spent managing email infrastructure


One of the biggest differences was how naturally Halon fit into Rule’s existing development processes. Configuration could be managed as code and deployed through Rule’s CI/CD workflows, aligning email infrastructure with the way the wider engineering organization already worked.

“My developers love how they could have everything in code, how we can deploy everything just in our whole CI/CD system. It just works.”

With leaner configurations, automated processes, and fewer manual interventions, Rule now spends 40% less time managing its email infrastructure. The improvement has also shifted responsibility from the CEO to Rule's backend and DevOps teams, reducing reliance on individual knowledge and freeing time for more valuable work.

70% faster implementation of delivery policies


Under Rule's previous PowerMTA configuration, managing different sending speeds meant maintaining multiple versions of the same IP pools. Years of accumulated configuration made even relatively straightforward changes more complicated than they needed to be.

With Halon, Rule can now apply rate limits directly to individual customers without recreating those configurations. When one customer requested a limit of 200 emails per minute, the team implemented it with a single line of policy configuration.

This greater flexibility has helped Rule reduce the time needed to implement delivery policies by 70%, making it easier to respond to changing customer requirements without adding unnecessary complexity.

"This is great news, and something we couldn’t do in PowerMTA. With Halon, it actually just works. Our configs are so much leaner now, which helps us enormously with getting insight into what deliverability issues we have and what works. It makes our DevOps work so much easier.”

50% faster identification and resolution of delivery issues


Simplifying the infrastructure has also improved Rule's ability to understand what's happening across its email operations. With Halon, Rule's leaner configuration gives its DevOps team greater visibility into different IP segments, delivery behavior, and potential problems.

As a result, Rule can now identify and resolve delivery issues 50% faster, helping its team spend less time troubleshooting and more time maintaining reliable email delivery for customers. For a platform serving more than 3,700 customers, that improved operational visibility makes it easier to maintain the dependable service customers expect.

Eliminated legacy email infrastructure risk


Rule no longer depends on a platform whose long-term direction had become a concern for the business. Its core email streams now run on modern email infrastructure backed by a team it trusts, around the clock.

"Everybody knows that day will come. The question is how prepared you are, and how much risk you're willing to take. You don't switch your main server in an hour."

New features for Rule's own customers


Halon is also helping Rule add features to its own product. Rule's platform can send Halon a message and the time it should go out, and Halon holds it in the queue until then. Rule used this to launch send-time optimization for its customers in 2026.

Headroom for growth and peak season


Rule is sending more email every day, and Halon handles it without bottlenecks. Rule's hardware is deliberately oversized, and when Sam checks, CPU often sits at around 2%. Hardware is a rounding error in Rule's infrastructure budget.

"We're growing and sending more emails every day, and with Halon we don't see any bottleneck. The hardware costs are pennies and cents compared to everything else in our infrastructure."

That headroom matters most during peak season. For any platform sending email at scale, the run-up to Black Friday and the holidays is usually the most nerve-racking stretch of the year. Now that Rule’s email runs on Halon, delivery is the one part of its stack Sam doesn’t worry about. There’s no firefighting and no daily check-ins on IP ranges, because it just works.


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The takeaway for anyone still on PowerMTA


Rule's story isn't that PowerMTA broke. It's that a platform that "just works" can still be the biggest unmanaged risk in your business, especially when its ownership, roadmap, or long-term fit no longer gives you confidence. Rule moved before it had to, on its own timeline, and found the switch easier than expected.

It's just an unnecessary risk to take. And it's not hard to make the switch. I'm a 100% supporter and fan of Halon.

Sam panel

Sam Jahanfar, CEO, Rule

Still running PowerMTA? Modernizing doesn't have to mean disruption. See how Halon can help you simplify operations, gain control, and migrate on your own terms.

Explore Halon vs. PowerMTA