# Team chat tools compared: Slack, Microsoft Teams, Mattermost and Rocket.Chat

> Four team chat tools in an editorial comparison: two cloud services and two self-hosted platforms, assessed on data protection, security, operation and pricing model.

- URL: https://saascolumn.com/en/compare/team-chat-tools-comparison/
- Author: [SaaS Column Editorial Team](https://saascolumn.com/en/author/editorial-team/), Editorial team
- Published: 13 November 2026
- Other languages: DE https://saascolumn.com/vergleich/team-chat-tools-vergleich/

## In short

For companies on Microsoft 365, Teams is the obvious choice, not least because of the EU Data Boundary. Slack has the strongest app selection, but EU data residency only from Business+. If you want data sovereignty and have Linux skills, Mattermost is the best fit. Rocket.Chat suits small self-hosting teams of up to 50 users.

Which team chat tool suits a small or mid-sized business in Europe? We compare Slack, Microsoft Teams, Mattermost and Rocket.Chat based on publicly documented features, privacy documentation and pricing models as of November 2026.

## Ranking

### 1. Microsoft Teams

Best for: Companies on Microsoft 365

The best choice if Microsoft 365 is already in use: EU Data Boundary, ISO 27001 scope and integration with Outlook and SharePoint.

**Pros**

- EU Data Boundary for EU and EFTA customers
- Chat, meetings and files in one tool
- Teams Essentials as an affordable entry

**Cons**

- Free version for personal use only
- Ties you to the Microsoft ecosystem

### 2. Slack

Best for: Cloud teams with many third-party apps

Excellent usability and a large app directory. EU data residency and SAML SSO require the Business+ plan, though.

**Pros**

- Free plan to get started
- Broad evidence including a C5 attestation

**Cons**

- Data residency only from Business+
- Member profiles not covered by residency

### 3. Mattermost

Best for: Data sovereignty through self-hosting

The most mature self-hosted option in this comparison, with SOC 2 Type II and ISO 27001. Requires operational know-how.

**Pros**

- You choose the server location
- Professional with SSO for up to 250 users

**Cons**

- Own operating effort
- Entry has limited history

### 4. Rocket.Chat

Best for: Small self-hosting teams up to 50 users

Flexible and generous on the Starter plan. Missing price information and no DPF entry make it harder to assess.

**Pros**

- Starter with SAML free for up to 50 users
- Matrix federation in enterprise plans

**Cons**

- Prices on request only
- No entry found on the DPF List

## Criteria

- **Features and integrations**: Channels, threads, calls, apps and APIs according to the documentation.
- **Data protection and location**: DPA, EU data location, legal basis for international transfers.
- **Security and evidence**: SSO, MFA, certifications and audit reports.
- **Operation and effort**: Cloud or self-hosted, IT skills required.
- **Pricing model and entry**: Free plan, billing model, upgrades needed for key features.

The ranking is an editorial assessment. It is based on publicly documented features, pricing pages, the vendors' privacy and trust documentation and a check of the DPF List on 13 November 2026. We did not carry out a long-term hands-on test.

Data protection, data location and features carry the most weight. The full criteria and weights are published on [How we evaluate software](https://saascolumn.com/en/how-we-evaluate-software/).

In many companies, team chat has replaced internal email. That means customer data, HR questions and supplier discussions end up there too. Choosing a tool is therefore a data protection decision. We compare four widely used options: two US cloud services and two open source platforms you can host yourself.

## Cloud or your own server?

**The key question is the operating model.** Slack and Microsoft Teams run only as cloud services. You need no in-house IT, but your data goes to a US vendor. Mattermost and Rocket.Chat run on your own servers or with a hosting provider of your choice. You decide the location, but you are responsible for updates and security.

For cloud services you need a [data processing agreement](https://saascolumn.com/en/blog/data-processing-agreement-saas/) and a legal basis for transfers to the US. Slack, Microsoft and Mattermost were listed as active on the [EU-US Data Privacy Framework](https://saascolumn.com/en/blog/eu-us-data-privacy-framework-saas/) List when we checked on 13 November 2026. Slack is covered as an entity of Salesforce. We found no entry for Rocket.Chat. The vendor uses standard contractual clauses in its DPA.

## The four tools at a glance

|  | Slack | Microsoft Teams | Mattermost | Rocket.Chat |
| --- | --- | --- | --- | --- |
| Deployment | Cloud | Cloud (Microsoft 365) | Self-hosted, Cloud Enterprise on request | Self-hosted, dedicated cloud |
| Free entry | Free: 90 days of history, up to 10 apps | personal version only, Teams Essentials for business | Entry (10,000 messages of history) or Team Edition | Starter up to 50 users, Community |
| EU data location | region selectable from Business+ | EU Data Boundary | your own server | your own server |
| SAML SSO | from Business+ | via Microsoft Entra ID | from Professional | from Starter |
| Evidence (per vendor) | ISO 27001, SOC 2 Type II, C5 | ISO 27001 (Office 365) | ISO 27001, SOC 2 Type II | SOC 2 Type II |
| DPF List (13 Nov 2026) | active (via Salesforce) | active | active | no entry found |

Information as of November 2026, based on the vendors' pricing, help and trust pages. We did not run the tools in long-term operation. The evidence column reflects what the vendors publish themselves.

## How do the cloud services differ?

**Slack stands out for its app directory and usability, Teams for its Microsoft integration.** According to Slack's [help centre](https://slack.com/help/articles/360035633934-Data-residency-for-Slack), data residency in a region such as Frankfurt requires Business+. Even then, member profiles and memberships are excluded. The free plan shows only 90 days of message history.

With the [EU Data Boundary](https://learn.microsoft.com/en-us/privacy/eudb/eu-data-boundary-learn), Microsoft has committed to storing and processing customer data of Microsoft 365 customers from the EU and EFTA within that region. Microsoft documents the exceptions. Following commitments accepted by the European Commission on 12 September 2025, Microsoft offers suites with and without Teams in the EEA (reported by heise online, among others).

Both cloud vendors publish audit evidence. On its [compliance page](https://slack.com/trust/compliance), Slack lists ISO/IEC 27001, SOC 2 Type II and a C5 attestation from the German BSI, among others. Microsoft includes Teams in the ISO 27001 scope of Office 365. For small businesses, such evidence is often the only practical way to assess a vendor's security.

## How do the self-hosted options differ?

**Mattermost is the more mature platform for small and mid-sized teams, Rocket.Chat the more flexible one for federation.** Mattermost offers a free Entry edition with all features but a history limit of 10,000 messages. The Professional plan covers up to 250 users with SSO and support. Details are in our [Mattermost review](https://saascolumn.com/en/review/mattermost-review/).

Rocket.Chat's Starter plan is free for up to 50 users and already includes LDAP and SAML. The enterprise plans add Matrix federation and end-to-end encryption, with prices on request only. The vendor itself does not consider the Community edition suitable for business-critical use.

## What about calls and meetings?

**All four tools offer calls, but to different extents.** Teams includes full meetings. Mattermost has its own Calls feature, which is due to be limited to 40 minutes in the free Entry edition. According to its documentation, Rocket.Chat integrates Jitsi and BigBlueButton, and from Starter also Zoom, Google Meet and Pexip. With the cloud services, calls run on the vendor's infrastructure.

Video conferencing has its own data protection rules, for example on recording and default settings. Our checklist on [GDPR-compliant video conferencing](https://saascolumn.com/en/blog/video-conferencing-gdpr-compliance/) sums them up. Also look for [single sign-on](https://saascolumn.com/en/glossary/single-sign-on-sso/) in every tool. It lets you revoke access for leavers in one central place.

## Which tool suits whom?

- **Microsoft Teams:** companies already on Microsoft 365 that want chat, meetings and files in one place.
- **Slack:** cloud teams with many third-party apps that are willing to pay for Business+ to get EU data residency.
- **Mattermost:** businesses with Linux skills or a hosting partner that want data sovereignty.
- **Rocket.Chat:** small teams of up to 50 users with self-hosting experience, or organisations that need federation.

Our [SaaS selection checklist](https://saascolumn.com/en/blog/how-to-choose-saas-tools-checklist/) shows how to structure the decision. More comparisons are listed on our [comparisons overview](https://saascolumn.com/en/comparisons/).

There is no best tool for everyone. Two questions decide: do you use Microsoft 365, and can you run your own server? Answer them first and the shortlist quickly shrinks to one or two candidates.

*Disclosure: No paid placements, no affiliate links.*

## Frequently asked questions

### Which team chat tool is GDPR-compliant?

None is compliant by itself. Compliance comes from a DPA, a legal basis for international transfers and suitable settings. Self-hosting Mattermost or Rocket.Chat gives you the most control over data location.

### Can I use Slack with servers in Germany?

Yes, from the Business+ plan. Slack offers data residency in Frankfurt there, with backups in Paris. According to Slack, member profiles and some metadata are excluded.

### Is Microsoft Teams free for businesses?

The free version of Teams is intended for personal use. For businesses, Microsoft offers Teams Essentials or Microsoft 365 suites on subscription.

### How much does Mattermost cost?

Mattermost Entry and Team Edition are free. According to the vendor, the Professional and Enterprise plans are billed as prepaid annual subscriptions per seat.

## Sources

1. [Slack pricing](https://slack.com/pricing), Slack
2. [Data residency for Slack](https://slack.com/help/articles/360035633934-Data-residency-for-Slack), Slack
3. [Slack compliance certifications](https://slack.com/trust/compliance), Slack
4. [What is the EU Data Boundary?](https://learn.microsoft.com/en-us/privacy/eudb/eu-data-boundary-learn), Microsoft
5. [ISO/IEC 27001 – Microsoft Compliance](https://learn.microsoft.com/en-us/compliance/regulatory/offering-iso-27001), Microsoft
6. [Microsoft Teams Essentials QuickStart guide for small businesses](https://learn.microsoft.com/en-us/microsoftteams/get-started-with-teams-essentials), Microsoft
7. [Einigung: EU und Microsoft vereinbaren neue Auflagen für Teams](https://heise.de/-10643365), heise online, 2025-09-12
8. [Editions and Offerings](https://docs.mattermost.com/product-overview/editions-and-offerings.html), Mattermost
9. [Mattermost pricing](https://mattermost.com/pricing/), Mattermost
10. [Mattermost Trust Center](https://trust.mattermost.com/), Mattermost
11. [Rocket.Chat pricing](https://www.rocket.chat/pricing), Rocket.Chat
12. [Our plans](https://docs.rocket.chat/docs/our-plans), Rocket.Chat
13. [Rocket.Chat achieves SOC 2 Type II attestation](https://de.rocket.chat/blog/rocket-chat-achieves-soc-2-r-type-ii-attestation), Rocket.Chat, 2026-02-23
14. [Data Processing Agreement (GDPR)](https://docs.rocket.chat/docs/data-processing-agreement-gdpr), Rocket.Chat
15. [Data Privacy Framework List](https://www.dataprivacyframework.gov/list), International Trade Administration, U.S. Department of Commerce