Slack started out as a video game. Mattermost started out as an internal tool built to fix the problems of another corporate chat app. Neither was born with data sovereignty in mind, but fifteen years later both represent two opposite models of who controls a company's internal conversations: a platform managed by one of the largest US tech companies, and free software that any organisation can host wherever it chooses.
Comparisons between Slack and Mattermost usually stop at chat features, integrations and per-user pricing. Here we ask a different question: when your team discusses a confidential negotiation, a security incident or a strategic decision over chat, which country does that conversation live in, and which law decides who can request access to it?
Slack: from a failed video game to Salesforce infrastructure
Slack Technologies was founded in 2009 in Vancouver, Canada, as Tiny Speck, the gaming company started by Stewart Butterfield — previously a co-founder of Flickr. The internal chat tool the team built to coordinate while developing the video game Glitch turned out to be more valuable than the game itself. When Glitch shut down in 2012, the team pivoted entirely to that messaging tool, which launched publicly as Slack in 2013, with the company's legal name changing in 2014.
In December 2020, Salesforce announced its acquisition of Slack for $27.7 billion, closing in July 2021. Since then, Slack has operated as part of Salesforce, headquartered in San Francisco, United States (EIU 7.85). Slack's Canadian origins — Canada scores 8.89 on the EIU index, a full democracy — are now a historical footnote: the infrastructure, the legal parent company and the jurisdiction governing your data are fully American.
Why jurisdiction matters in a company chat
The 2018 CLOUD Act allows US authorities to request data stored on the servers of US tech companies, regardless of which country those servers physically sit in. Salesforce offers EU data residency options for Slack Enterprise Grid, but the parent company still ultimately answers to US law, in the same way as Google, Atlassian or Twilio.
A company's chat history is not a minor piece of data: it includes credentials shared by mistake, contract drafts, layoff discussions, security incidents and commercial strategy. For regulated sectors — banking, defence, healthcare, public administration — the jurisdictional location of that history is part of the risk analysis, not just a product choice.
Mattermost: open messaging you decide where to host
Mattermost Inc. traces back to SpinPunch, a gaming company founded in San Francisco in 2011. In 2014, its team ran into the same problem Slack had already solved for itself years earlier — they needed reliable internal chat — and in 2015 they open-sourced the code. Although the company that maintains Mattermost is also American, the product itself is software that any organisation can deploy on its own server, in any country.
That possibility isn't theoretical: customers running self-hosted Mattermost include European industrial manufacturers like Airbus, financial institutions like ING Bank (Netherlands, EIU 9.01), and large German industrial groups like Bosch and Daimler (Germany, EIU 8.58), alongside organisations such as CERN, headquartered in Switzerland (EIU 9.12). For these organisations, the self-hosted option keeps internal chat under the same jurisdiction as the rest of their critical infrastructure.
Democratic analysis: two ways of solving the same risk
Applying Democratic Market's criteria, neither Slack nor Mattermost is excluded by origin: Salesforce and Mattermost Inc. both operate from the United States, with an EIU score of 7.85, comfortably above the 6.0 threshold. The democratic difference isn't the nationality of the company that builds the software, but whether the end customer can decouple product use from the manufacturer's jurisdiction.
With Slack, that decoupling is limited: you can pin the storage region within the options Salesforce offers, but the infrastructure remains company-managed and subject to its legal framework. With self-hosted Mattermost, the decoupling is total: the server, the hosting provider and the applicable law are chosen entirely by the user organisation, with no dependency at all on Mattermost Inc.'s jurisdiction.
The practical result is that a German company can run Mattermost hosted in a Frankfurt data centre operated by a German company, falling under exclusively European jurisdiction, while that same company using Slack will still ultimately depend on US law, however many residency options it activates.
This difference gets worse in merger or acquisition scenarios. Slack went from being an independent Canadian company to part of Salesforce within months of the deal being announced; its customers had no say whatsoever over that change of legal parent, nor over the jurisdiction their data suddenly fell under overnight. With self-hosted Mattermost, a change of ownership at the company maintaining the software doesn't alter, in any way, the infrastructure the user organisation already controls.
Message retention and regulatory compliance
For European financial firms, MiFID II requires retaining trading-related communications for a minimum of five years and being able to produce them to the supervisor on request. Slack Enterprise Grid covers this requirement through integrations with specialised third-party archivers such as Global Relay or Smarsh, which adds a third vendor — and a third jurisdiction to audit — into the compliance chain.
With self-hosted Mattermost, message history lives in the same database the organisation itself administers, under the same jurisdiction as the rest of its infrastructure. Retention, encryption and access for legal audit purposes are configured once, without depending on an additional archiving vendor or its own subcontracting chain.
Technical comparison: features, price and democratic profile
Slack offers a polished experience, an ecosystem of over 2,600 integrations, built-in audio and video huddles, and a very smooth adoption curve thanks to years of product refinement. Mattermost replicates most of those core features — channels, threads, video calls, webhook and API-compatible integrations — with an approach more geared toward technical teams, DevOps, and sectors with strict compliance requirements.
On price, Slack charges per user per month with limited message history on free tiers. Mattermost is free in its self-hosted open-source edition, and offers paid plans with support and additional security features for large organisations. The real cost of the self-hosted option sits in the server and maintenance time, not per-user licensing.
For incident management, Mattermost ships Playbooks out of the box, a feature built for DevOps and security teams that structures step-by-step response directly inside the chat. Slack offers similar capabilities through integrations with external tools like PagerDuty or Jira Service Management, but not as a native feature included in the base product.
Certifications and government deployments
Mattermost holds FedRAMP High authorisation through its partner FedHIVE and has been deployed in Impact Level 4, 5 and 6 environments for the US Department of Defense, as well as classified intelligence networks such as JWICS. It's by far the most demanding level of government certification among the tools in this comparison, precisely because the self-hosted model lets the infrastructure be adapted to fully air-gapped networks.
Slack, through Salesforce, maintains SOC 2 Type II and ISO 27001 certifications, and offers a dedicated public-sector offering for US government customers. But as a managed service, all of that certification lives inside infrastructure Salesforce controls: no customer organisation can deploy Slack on a fully air-gapped network the way it can with self-hosted Mattermost.
EU legislation that applies in 2026
For regulated sectors, the DORA regulation, in force since January 2025 for the financial sector, and the NIS2 Directive, currently being transposed across member states, require formally documenting the risk posed by third-party providers of critical internal communications. A bank or essential infrastructure operator using Slack must justify the US subcontracting chain to its supervisor; if it uses Mattermost self-hosted in Europe, that justification becomes substantially simpler.
How Democratic Market evaluates this kind of tool
We evaluate internal communication software with the same criteria we apply to any product: the company's country of origin, the EIU score of its jurisdiction, real data residency options and, especially relevant for software, whether a self-hosting path exists that fully decouples product use from the manufacturer's jurisdiction.
Neither Slack nor Mattermost Inc. is grounds for exclusion on democratic origin. Our recommendation isn't to systematically avoid American products, but to understand how much real control you have over each one and to exercise it when your use case justifies it.
This logic applies equally to any other internal communication tool we evaluate in the future: Microsoft Teams, Discord for communities, or any emerging European alternative. The question we always ask is the same, regardless of country of origin: can the end customer decide, based on verifiable facts rather than marketing promises, which law governs their most sensitive information?
This same effective-control criterion — beyond the company's nationality — is what we apply to any other software category we evaluate: the relevant question isn't only where the company was founded, but how much real capacity the end customer has to decide, change, or walk away from the infrastructure managing their most sensitive information.
It's a criterion that scales with what's actually being discussed, not a blanket rule against any single tool. A social committee planning the office party carries a very different risk profile from a finance team discussing an unannounced acquisition, and it's entirely reasonable for the same organisation to run both Slack and a self-hosted Mattermost instance side by side, routing each conversation to whichever platform's jurisdiction actually matches its level of sensitivity and confidentiality.
Mattermost, in short, isn't simply a cheaper alternative to Slack: it's a fundamentally different way of solving the same problem, built on an opposite philosophy of control.
None of this is meant to suggest Slack is unsafe to use — most teams, including plenty at European companies, run it every day without incident, and for general-purpose team chat with no special sovereignty requirement, it remains a perfectly reasonable default. The point is narrower: when the content of your conversations genuinely warrants a sovereignty decision, know which product actually lets you make one, and which one only lets you configure around the edges of a decision someone else already made. Knowing the difference in advance beats discovering it during an audit.
Whichever you choose, revisit the decision whenever your organisation's risk profile changes — a new regulated client, a new government contract, a new class of information flowing through the chat. A tool that was a perfectly reasonable default last year may no longer be the right one once what you're discussing in it changes. Build that review into your annual vendor risk assessment rather than waiting for an incident to force the conversation, and write the decision down so the next person doesn't have to relitigate it from scratch.
Practical buying guide
If your team is small, doesn't handle especially sensitive information, and prioritises the best possible user experience, Slack remains a reasonable option: enable EU data residency options if Salesforce offers them for your plan, and periodically review its compliance documentation.
If your organisation operates in a regulated sector, handles confidential customer information, or simply prefers not to depend on US jurisdiction for its internal communications, evaluate self-hosted Mattermost on a European provider. The investment in infrastructure and maintenance is offset by full jurisdictional control.
Either way, define a clear retention and deletion policy for chat history, and avoid sharing credentials, contracts or sensitive personal data directly in chat, regardless of the tool chosen: no residency setting substitutes for good data hygiene.
It's also worth weighing the cost of changing your mind later. Migrating full chat history from Slack to Mattermost, or vice versa, is technically possible through export and import tools both platforms document, but it's worth planning ahead: the larger the accumulated history and the more integrations depend on each product's specific API, the greater the migration effort if you decide to change jurisdiction down the line.
Finally, neither tool on its own solves the problem of data employees themselves upload into channels or threads: screenshots, attached documents, meeting recordings. That layer of content deserves the same sensitivity-classification policy as the rest of your corporate information, and its jurisdictional location ultimately depends on where the chosen chat platform is hosted.
Conclusion: the conversation also has a legal address
Slack and Mattermost start from the same country and the same democratic score, but offer radically different levels of control over where your company's conversation lives. One lets you flip on options within a framework that remains its own; the other hands you the keys entirely. Knowing which one you need depends on what you discuss in that chat, not just how many integrations it has — and that's a question worth asking before the conversation gets sensitive, not after.
This article was originally published at Democratic Market. Read the full version with additional analysis on our site.
