Migrating from Slack to Mattermost is a strategic move for organizations looking to reclaim control over their communication data, eliminate escalating per-user subscription fees, and meet stringent data residency requirements. While Slack is a powerful proprietary tool that charges between $7.25 and $15 per user per month, Mattermost offers a robust, open-source alternative that can be self-hosted on your own infrastructure for free, with enterprise-grade scaling options available.
Organizations typically initiate this migration when they hit Slack's message history limits on free tiers, when compliance mandates require keeping all message archives and file attachments on-premise, or when engineering teams want deep integration capabilities without paying for higher Slack pricing tiers. Moving from Slack's closed cloud ecosystem to Mattermost allows IT administrators to customize the source code, secure proprietary workflows behind corporate firewalls, and significantly reduce operational software expenditures.
However, transitioning away from Slack requires careful planning regarding channel structures, user identity mapping, and historical data preservation. Because Mattermost uses a PostgreSQL or MySQL backend and a different API schema than Slack, the migration path involves specialized translation tools and administrative oversight to ensure a seamless experience for end users accustomed to Slack workflows.
For a 50-person team that's a significant annual saving.
🗺️ Migration Steps
Begin by exporting your workspace data from Slack through the workspace settings dashboard if you are on an eligible plan. This generates a ZIP archive containing JSON files for public channels, direct messages, and uploaded files. Keep in mind that Slack restricts exports of private channels and direct messages depending on your workspace subscription level.
Set up your target Mattermost environment by deploying the application via Docker, Kubernetes, or a direct Linux installation connected to a PostgreSQL or MySQL database. Configure your domain, set up TLS certificates, and establish SAML or LDAP authentication to match your identity provider before importing any data.
Use community-maintained migration scripts or the Mattermost bulk load tool to process your exported Slack JSON files. You must map Slack user IDs and email addresses to your new Mattermost user accounts to preserve message authorship and maintain direct message continuity after the import.
Import the transformed JSON data into your Mattermost database using the mattermost import bulk command-line tool. This populates your teams, public channels, and historical messages into the new server instance while verifying data integrity against your database schema.
Recreate your critical workflows by migrating Slack incoming webhooks, slash commands, and custom integrations to Mattermost equivalents. Mattermost supports most Slack-compatible webhook formats, though you may need to update endpoint URLs and adjust authorization tokens for custom bots.
Invite your team members to the new Mattermost instance, instructing them to log in using your configured SSO provider and download the desktop or mobile clients. Once users have verified their access and channels, lock down the Slack workspace to officially complete the cutover.
⚠️ Common Challenges & How to Avoid Them
Upgrade your Slack workspace temporarily to a plan that permits complete data exports, or communicate to your team that historical private chats will start fresh in Mattermost.
Write a custom script to download file links from the Slack export manifest and upload them directly into your Mattermost file storage backend during the migration window.
Enable Slack-compatible shortcut settings in Mattermost and prepopulate the custom emoji pack using your most popular Slack reactions before launch day.
🔗 Get Started
❓ Frequently Asked Questions
Yes, public channel message history can be migrated using JSON export tools and bulk loaders. However, migrating file attachments requires extra scripting because Slack exports only provide downloadable URLs rather than the raw files themselves.
Mattermost offers a free, fully functional open-source edition that you can self-host indefinitely without per-user fees. Slack charges between $7.25 and $15 per user per month for standard paid tiers, making Mattermost significantly more cost-effective for large organizations.
Many Slack-compatible incoming and outgoing webhooks work out of the box because Mattermost supports a similar payload format. However, complex Slack Apps built on Bolt framework or specific Slack APIs will need to be rewritten or reconfigured for the Mattermost plugin architecture.
Want a full feature and pricing comparison before you switch?
Read the Full Slack vs Mattermost Comparison →