Encrypted Slack Alternative: Open-Source Mattermost with EU Data Control
E2E encryption. GDPR-compliant. No per-user pricing. Deploy in minutes on Opsily hosted in certified German data centers.
Why Teams Are Leaving Slack for Encrypted Alternatives
Slack runs on AWS, a US company governed by the CLOUD Act. Your messages, files, and metadata flow through American servers and can be accessed by law enforcement without a warrant.
If you operate in healthcare, finance, government, or regulated industries, this is a legal and compliance problem. Even for smaller teams, privacy matters. Slack also charges $7.25 per user per month, for a 50-person team, that's €3,625 per year, with zero encryption.
Encrypted Slack alternatives exist. The question is which one: open-source or proprietary? EU-hosted or cloud-only? Flat-rate or per-user pricing?
Mattermost answers all three.
Encrypted Slack Alternatives Compared
Compare encrypted Slack alternatives: Mattermost vs. Element, Wire, and Stackfield on encryption, pricing, and hosting.
Element pricing not public (contact sales). Opsily pricing as of 2026-11-09. All platforms offer encryption; differences are in availability tier, hosting model, and cost structure.
The Encrypted Slack Alternative That Actually Works
Element is strong on encryption (full E2E by default), but it requires you to self-host or pay opaque per-seat pricing from a vendor. Wire is proprietary and costs €7.45 per person per month. Stackfield is German-only and hides pricing behind a trial signup.
Mattermost sits in the sweet spot:
E2E Encryption Available: Available in Enterprise and Enterprise Advanced tiers. Once enabled, only sender and recipient can decrypt messages. Files, calls, and history are included.
At-Rest Encryption Standard: On Opsily, all data is encrypted with AES-256 in transit (TLS 1.3) and at rest. Backups are encrypted separately and stored for 3 months.
Open Source, Auditable Code: Mattermost's MIT license means the full source code is public on GitHub. No proprietary black box. 39.6K GitHub stars and 23,866 commits show active development and community trust.
GDPR + EU Hosting Default: Opsily stores all data in ISO 27001-certified data centers in Germany, Netherlands, UK, and Finland. No US jurisdiction. Data Processing Agreements are signed as standard.
Flat-Rate Pricing, No Per-User Cliff: At €99/month on Opsily, you pay the same whether you have 5 users or 100 users. Slack Pro would cost €362.50/month for the same team size.
Integrations That Just Work: Mattermost connects to 300+ tools: Jira, GitHub, GitLab, Slack, Zoom, PagerDuty, Sentry, and custom webhooks. DevSecOps teams automate incident response without leaving chat.
Why Opsily Delivers the Best Encrypted Slack Alternative
Not all managed Mattermost hosts deliver encrypted Slack alternatives. Here's what sets Opsily apart for teams requiring encryption and data control.
Encryption Built In
TLS 1.3 in transit, AES-256 at rest, daily encrypted backups in separate storage. E2E messaging available in Enterprise tier—just flip a switch. No add-on fees.
GDPR by Default
Data stays in ISO 27001-certified German, Dutch, UK, or Finnish data centers. No US transfers. Data Processing Agreements signed at signup. Automatic encryption means zero exposure.
Flat-Rate, No Lock-In
€99/month flat. No per-user scaling, no surprise bills, no contract. Mattermost is open-source MIT; export your data anytime. Opsily is just infrastructure. You own everything.
Built for teams who need reliability
Transparent Pricing. No Surprises.
All Opsily plans include daily encrypted backups, automatic security updates, 24/7 monitoring, GDPR DPA, and run on certified data centers.
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Saved per year vs Slack Pro for 50 users
Slack Pro costs €7.25/user/month × 50 users × 12 months = €4,350/year. Opsily Mattermost costs €99/month flat = €1,188/year. That's a 73% cost reduction.
Built for Privacy and Compliance
Teams in healthcare, finance, and government choose Mattermost on Opsily because encryption and data control aren't afterthoughts.
GDPR Compliant
Full GDPR compliance with Data Processing Agreements. Data stored in EU only. No US transfers. No CLOUD Act exposure.
Independently Audited Infrastructure
Data centers across Germany, Netherlands, UK, and Finland are independently audited for encryption, access controls, and security. Third-party verification of all controls.
Open Source Auditable
MIT-licensed Mattermost source code is public on GitHub. No hidden proprietary logic. Security researchers and your own team can audit the code.
E2E Encryption Ready
End-to-end encryption available in Enterprise tier. Messages, files, and calls encrypted so only sender and recipient can access.
No Vendor Lock-In
Mattermost is open-source. Export your data, database, and history anytime. Opsily is infrastructure; the app is yours to migrate.
Frequently Asked Questions
Common questions about encrypted Slack alternatives, Mattermost encryption, and Opsily managed hosting.
End-to-end encryption (E2E) means messages are encrypted on the sender's device and only the recipient can decrypt them. Even the hosting provider (Opsily) cannot read the messages. Mattermost offers E2E encryption in Enterprise and Enterprise Advanced tiers. Once enabled, all messages, files, and calls are encrypted. Slack does not offer E2E encryption; only transit and at-rest encryption.
Stop Paying Per User. Start Using Open-Source.
Deploy encrypted Mattermost on Opsily in minutes. GDPR-compliant EU infrastructure included.