Slack → Mattermost
What it saves, what actually moves, what you rebuild — and the thing that catches people.
What it costs, and what it saves
Slack Pro is about $8.75 per user per month; 30 people costs roughly $3,150 a year. Mattermost Team Edition is free and self-hosted.
Moves cleanly
Message history via Slack's export and Mattermost's bulk import — public channels transfer well, DMs need the paid Slack export.
You rebuild
App integrations, though Mattermost supports most through webhooks and its own marketplace.
What Slack costs you today
Per-user monthly plans; the free tier hides older message history
What actually holds you in
Cloud-only hosting and per-seat billing; your history and integrations sit on Salesforce's terms.
What you are moving to
Mattermost is an open-source, self-hostable Slack alternative with strong security and compliance features, popular with engineering and defense/regulated teams that need to own their data.
Free self-host; paid Enterprise
Mattermost strengths
- Purpose-built self-hosted Slack replacement
- Strong security/compliance story
- Familiar channel UX
What you give up
- You operate the server
- Some features are Enterprise-only
The migration, step by step
- 1Request the Slack export — the free tier only exports public channels, which is often the real constraint
- 2Deploy Mattermost with Postgres
- 3Run mmctl import to bring in the archive and verify threading survived
- 4Recreate integrations, starting with the ones that page people
- 5Move one team first and keep Slack read-only for a month rather than deleting it
The gotcha
Slack's free plan does not export DMs or private channels. If your organisation's real institutional memory is in DMs — and it usually is — that history does not come with you unless you pay Slack for a full export before leaving.
When to stay on Slack
Your workflow depends on Slack's app ecosystem, or huddles and Connect channels with other companies.
More Layer 5 migrations
Figures verified 2026-07-04 against vendor pricing pages. Prices change and migrations differ by estate — treat the cost delta as a starting model, not a quote. Rankings and recommendations here are merit-only; affiliate income never changes a verdict. See our methodology.