Slack vs Mattermost: which fits your team chat
Slack fits best when your team wants a managed cloud service, a large app ecosystem, built-in huddles and as little server administration as possible. Mattermost fits best when the main driver is control over where messages live, and when your organization has the admin capacity to run a self-hosted server. Renewals, per-seat pricing changes and data residency rules are the usual triggers for this comparison, and the answer depends on which controls your organization must have, not on which product is more popular.
Slack works well for teams that rely on its integrations, Huddles and managed upgrades, and that do not need the messages on their own infrastructure. Mattermost fits teams that want to run the platform in their own cloud account or data center. Its Team Edition is free and MIT-licensed as compiled by Mattermost, aimed at teams under 250 users that do not need single sign-on. Once you need SAML or OIDC single sign-on, AD/LDAP user sync, high availability or compliance export, you move to a paid tier. Mattermost sells Professional, Enterprise and Enterprise Advanced as annual subscriptions by seat, and it does not publish prices, so you should ask for a quote built from your seat count and the specific controls you need.
Make the decision in four steps: list the features your teams cannot work without, decide where message data must reside, count the people who will operate the server and its database, and map each required control to the Mattermost edition that includes it. Confirm the current feature matrix with Mattermost sales before you rely on any tier, and check that your admin team can handle upgrades, since Mattermost publishes a new server version each month and asks you to plan around its support windows. If a required feature sits in a paid edition, include that cost in your comparison alongside hosting and admin time.
Which platform fits which scenario
This table matches common Slack buyer situations to the Mattermost edition or deployment choice that fits best, with the reason tied to documented facts. Read each row against your own user count, identity requirements, data location and reliance on Slack apps, then confirm the edition details with Mattermost before you commit.
| Scenario | Better fit | Reason |
|---|---|---|
| Small team under 250 users, no SSO needed | Mattermost Team Edition | Free, open source and self-hosted, and aimed at teams under 250 users that do not need single sign-on. |
| Regulated organization needing SSO and compliance export | Mattermost Professional or Enterprise | SSO (SAML, OIDC, OAuth) starts at Professional, and compliance export is in paid Professional, Enterprise and Enterprise Advanced plans. Confirm which tier includes your exact compliance features. |
| Data must stay in your own datacenter | Self-hosted Mattermost | Mattermost runs as a single Linux binary with PostgreSQL, so data stays on infrastructure you control. Air-gapped deployment is listed for Enterprise Advanced. |
| Team dependent on Slack apps and Workflow Builder | Plan a rebuild before choosing | Mattermost's Slack migration does not move integrations, so apps and workflows need inventory and re-creation whatever the edition. |
| High availability for critical chat | Mattermost Enterprise or Enterprise Advanced | High availability clustering is available only on Enterprise and Enterprise Advanced, and needs shared file storage on each node. |
| Organization wants a managed vendor instead of self-hosting | Slack or a managed Mattermost plan | Self-hosting moves operation, patching and backup to your team. Confirm whether Mattermost offers a hosted option that fits your residency needs. |
| Team that needs Slack Connect with outside partners | Plan separate guest or federation design | Slack Connect channels do not migrate to Mattermost, so partner access needs its own design and security review. |
Who controls the data and the servers
Slack runs as a managed cloud service, so messages, files and workspace metadata are stored in Slack's infrastructure and managed by Salesforce's Slack team. Your organization chooses its plan and admin settings but does not choose the hosting provider or the physical location of the servers in the standard offering. Mattermost, in contrast, runs as a single Linux binary backed by PostgreSQL, so you decide where the application servers, database and file storage live: your own data center, a private cloud account or an EU provider you select. Messages and attachments stay inside whatever boundary you build.
- Application and database: Mattermost writes messages to a PostgreSQL database you operate, with backups under your own schedule.
- File storage: Attachments go to the local file system on a single node, or to Amazon S3, an S3-compatible service or NAS in a clustered setup.
- Backups and retention: Retention is whatever your backup and policy configuration keeps, not a vendor default.
- Egress: Confirm which outbound connections the server makes, such as push notification relays, license checks and plugin downloads, and block or allow them deliberately.
Before committing, ask Slack which data residency options apply to your plan and region, and confirm the same questions with your own platform team for a self-hosted build.
With Slack, the vendor operates the platform: patching, scaling, uptime and infrastructure security sit in Slack's operations. Your admins manage workspaces, members, channels, apps and policies inside the admin console. With Mattermost, your team installs, upgrades, patches, monitors and backs up the server, so operational responsibility moves in-house or to the implementation partner you contract. Mattermost publishes a new server version each month on the 16th, with extended support releases on a longer cycle, so upgrade planning becomes a recurring task.
- Upgrade cadence: Mattermost v11.11 was released on 2026-09-16 with support ending 2026-12-15, so plan on regular version moves rather than occasional ones.
- Extended support: v11.7 is an Extended Support Release, released on 2026-05-15 with support ending 2027-05-15, which lowers how often you must move.
- Incident response: Your on-call rota, not the vendor's, handles outages on a self-hosted instance.
- Staffing: Count the database, Linux and application skills needed to run the stack, including after staff changes.
Ask your team who owns each of these functions on day one, and whether a support retainer covers the gaps.
Slack authenticates members through its own sign-in and supports enterprise single sign-on on higher plans, while your identity provider remains the source of truth for who is employed. Mattermost connects to your identity estate directly. According to the Mattermost pricing page, SSO through SAML, OIDC and OAuth and AD/LDAP user sync are included from the Professional plan. High availability clustering and FIPS 140-3 compliance require Enterprise, and air-gapped deployment requires Enterprise Advanced. Confirm which of these your identity model needs before you select an edition.
- Single sign-on: Mattermost's SAML single sign-on documentation describes the configuration path for identity providers that support SAML.
- Directory sync: AD/LDAP sync keeps accounts and deprovisioning tied to your directory on the Professional plan and above.
- Admin accounts: Keep at least one break-glass local admin, documented and tested, so an identity outage does not lock out the platform.
- Logout and session policy: Set session lifetimes in line with your own security standard.
Where your identity provider is also self-hosted, check whether it runs in the same network zone as Mattermost, because that changes the dependency and failure chain.
Hosting in your own environment gives you direct control over where evidence, logs and records are kept, but it does not make your deployment compliant by default. Slack's compliance features and export tools are part of a managed product whose assurance reports you can request from Slack. A self-hosted Mattermost deployment becomes assessable only when you build and document its controls yourself, or with an independent assessor. DeployOpen prepares systems, controls and evidence for compliance assessments, but it does not issue audit reports, attestations or certifications. Independent auditors and certification bodies do that work.
- Assurance documents: Ask Slack for its current third-party assurance reports and check their scope against your use.
- Compliance export: On Mattermost, compliance export and retention sit in paid editions, so budget for them if your policy requires them.
- Export rights on Slack: Every plan can export messages and file links from public channels, but private channels and direct messages require Business+ or Enterprise, and custom exports by member or conversation are Enterprise-only.
- High availability storage: A Mattermost cluster needs shared file storage on S3, an S3-compatible service or NAS mounted on each node, because local file system storage will not work correctly and risks corrupting files.
Ask your auditor which evidence they will accept for each control before you choose a hosting model.
Mattermost licensing and editions explained
Mattermost's editions decide which features you get for free, so confirm the edition before you compare costs with Slack. Team Edition is free, self-hosted and MIT-licensed as compiled by Mattermost, and it is aimed at teams under 250 users that do not need single sign-on. The commercial build has an Entry tier that is also free but caps channel message history at 10,000 messages and omits compliance features and high availability. Above Entry, Professional, Enterprise and Enterprise Advanced are sold as prepaid annual subscriptions priced by seat licenses. The Mattermost pricing page lists no public prices and directs buyers to sales, so you will need a written quote that names the seat count and the edition.
Source code is licensed separately from the binaries. Mattermost's source is available under AGPL v3.0 or under a commercial license from Mattermost, Inc., and admin tools and configuration files fall under Apache 2.0. Ask your legal team which license applies to the build you plan to run, especially if you intend to modify the server or distribute a custom build. Before you sign, ask the vendor to map each feature you need, such as SAML or OIDC single sign-on, AD/LDAP user sync, compliance export, clustering, FIPS 140-3 compliance and air-gapped deployment, to a specific edition in writing. The pricing page places SSO and directory sync from Professional, clustering and FIPS from Enterprise, and air-gapped deployment in Enterprise Advanced, but the contract is the authority.
Plan upgrades around the release calendar. Mattermost publishes server binaries on the 16th of each month, and the releases page states support end dates for each version. Mattermost v12.0 was released on 2026-10-16 with support ending 2027-01-15, and v11.11 was released on 2026-09-16 with support ending 2026-12-15. v11.7 is an Extended Support Release, released on 2026-05-15 with support ending 2027-05-15. Check whether your edition includes ESR support and who pays for upgrade testing, because a monthly cadence means you need a repeatable staging and rollback routine to stay within a supported version.
What drives the cost on each side
Slack bills per seat and ties some history and export rights to the plan you pick. Self-hosted Mattermost moves the cost into licenses for paid editions, servers, storage and the people who run them. The cards below separate one-time work from recurring spend so you can ask each vendor for the same breakdown.
Slack seats and plan dependence
Slack charges per user on a plan you choose, and the plan decides what you can keep and export. Free workspaces keep 90 days of visible history and lose content older than one year. Exporting private channels and direct messages requires Business+ or Enterprise, and custom exports by member or conversation are Enterprise-only. Ask the vendor which plan covers your retention and legal needs, and price that tier, not the entry tier. Recurring: seat fees for every licensed user, including guests and inactive accounts you still pay for.
Mattermost paid edition licenses
Team Edition is free and MIT-licensed, but it does not include single sign-on. SSO and AD/LDAP sync start with the Professional plan, high availability clustering and FIPS 140-3 compliance start with Enterprise, and air-gapped deployment is in Enterprise Advanced. These are prepaid annual subscriptions priced by seat licenses, and Mattermost lists no public prices. Recurring: renewal of seat licenses each year. In the quote, ask which edition each required feature sits in and whether seat counts include guests and deactivated users.
Hosting for database, storage and HA nodes
A Mattermost server runs as a single Linux binary on PostgreSQL. A high availability cluster needs redundant application servers, redundant database servers and redundant load balancers, plus shared file storage on Amazon S3, an S3-compatible service or NAS. Local file storage will not work correctly in a cluster and risks file corruption. Read replicas and search replicas add more nodes as users grow. Recurring: compute, storage, backups and database licensing if you choose a commercial PostgreSQL. Ask your infrastructure team to size each tier before you compare totals.
Monthly upgrade and administration effort
Mattermost releases a new server version in binary form on the 16th of each month, and each release has a support window. Extended Support Releases give a longer window, so ask which track your team will run. Someone must schedule upgrades, test integrations, watch database migrations and keep backups current. This work is the largest recurring internal cost on the self-hosted side and it does not appear on a Slack invoice. Estimate it as a standing share of an engineer's time, and confirm whether your vendor or partner offers it as a retainer.
Migration effort for history and integrations
Mattermost's Slack path converts an export with mmetl and loads it with mmctl. Users, channels, direct messages, threads and attachments move, but integrations, custom emoji images, user groups and Slack Connect channels do not. Your Slack apps, bots and workflows must be inventoried and rebuilt, and the people who own them need time for testing. This is typically a one-time cost, but it grows with the number of custom integrations. Ask the quote to list each Slack integration with a rebuild plan and to state how the export will be obtained.
Implementation and support services
Vendors and implementation partners charge for setup, hardening, integration work and ongoing support, which are separate from the software license. Fixed-scope implementation is usually a one-time cost with agreed deliverables, while support and upgrades are often retainers that recur. Confirm in writing what the partner covers, including backup testing, incident response windows and who applies monthly upgrades. Also confirm whether Mattermost support is bundled with your paid edition or sold separately. A written scope lets you compare self-hosted totals with a Slack renewal on equal terms.
What a move from Slack to Mattermost involves
The sequence below takes a Slack workspace from plan review to a cut over on self-hosted Mattermost, with a checkpoint at each step so the team knows what has moved and what still needs rebuilding.
Confirm the Slack plan and export scope
Before anything else, the workspace owner checks which Slack plan is active and what history the team needs. Every plan can export messages and file links from public channels, but private channels and direct messages need a Business+ or Enterprise plan, and custom exports by member or conversation are Enterprise-only. Done when the team has written down which conversation types must be included and whether the current plan covers them, or has opened the approved export request if it does not.
Run the Slack export and check its contents
A Slack workspace owner or admin runs the export and receives the archive. The platform or migration lead opens it and confirms that the expected public channels, private channels, direct messages and attachments are present, and notes any gaps. Done when the team has a complete archive stored in an access-controlled location and a short list of conversations that did not export.
Convert the export with mmetl and load it with mmctl
The migration engineer uses Mattermost's mmetl tool to convert the Slack export into Mattermost's bulk import format, then loads the result into a staging Mattermost server with mmctl. Users, channels, direct messages, threads and attachments move in this path. Done when the import log shows no blocking errors and staging channels, members and threads match a sample checked against the original Slack workspace.
Inventory and rebuild integrations, bots and commands
Slack integrations do not come across in the export, so the platform team lists every app, slash command, incoming webhook and bot in use, with its owner and purpose. Each one is rebuilt or replaced on Mattermost and tested in staging, including any custom emoji images and user groups that must be recreated by hand. Done when every inventoried item has a named owner and a tested Mattermost equivalent, or a documented decision to retire it.
Re-create user groups and plan Slack Connect channels
User groups are not migrated, so administrators recreate them in Mattermost and map memberships to the groups that drive mentions and channel access. Slack Connect channels shared with outside organizations do not move either. The team decides, per channel, whether to recreate it with guest accounts, move the conversation to another route, or archive it, and confirms the decision with the partner or customer. Done when the group list is verified and each Slack Connect channel has a recorded disposition.
Configure SSO, identity sync and file storage
Identity and infrastructure work happens before users arrive. The identity team connects Mattermost to the corporate identity provider for single sign-on and sets up user sync, both of which sit in paid Mattermost editions, so the team confirms its edition first. Storage for files is set up on shared, supported storage, because a multi-node high availability cluster needs shared file storage on Amazon S3, an S3-compatible service or NAS, and local storage will not work correctly. Done when test users sign in through SSO and an uploaded file is readable from every node.
Run a pilot with a small group of users
A defined group of users from a few teams works in the new Mattermost instance for a fixed period agreed in advance. The team collects issues on logins, notifications, file access, bots and migrated history, and fixes them in staging before the full cut over. Done when the pilot group has signed off on the core workflows and the open issues have owners and fixes scheduled.
Cut over and retire the Slack workspace
The team sets a cut over date, runs a final delta import of conversations created after the first import, announces the change, and points users and integrations at the Mattermost server. Slack is kept read-only for reference while the team confirms the archive is retained under its own retention rules. Done when all active users are on Mattermost, the integrations inventory is closed, and the archive is documented in the team's records.
Questions buyers ask before switching from Slack
What does it cost to run Mattermost compared with Slack?
Slack is a recurring per-user subscription, while self-hosted Mattermost Team Edition has no license fee, so the cost sits in hosting, administration and support. Mattermost's paid Professional, Enterprise and Enterprise Advanced plans are prepaid annual subscriptions priced by seat licenses, and its pricing page lists no public prices, so you will need a quote from Mattermost sales. The main drivers are server and database hosting, shared file storage and backups, the number of users, whether you need SSO or clustering, and the staff time to patch and upgrade. Ask for a total cost estimate that covers each of these components, not only the license line.
How long does a migration from Slack to Mattermost take?
The timeline depends on the size of the workspace, how much history you keep, and how much of the Slack setup you must rebuild. Mattermost moves a Slack export through the mmetl converter and mmctl, so the import itself is only one step among hosting setup, testing, user onboarding and cutover. Integrations, custom emoji images, user groups and Slack Connect channels do not move, so inventory them early because they often set the schedule. Your implementation partner should confirm a timeline in the written scope before work starts.
What does the work need from our own team?
You need named owners for identity, the Linux and database hosts, storage, networking and the business users who will test. On the identity side, SSO and AD/LDAP sync depend on your directory and certificates. Someone also has to own the Slack export, decide which private channels and direct messages come across, and approve the list of integrations to rebuild. Plan for regular upgrades, since Mattermost publishes a new server version each month and each release has a support end date, so the upgrade process needs an owner.
Can our own engineers run the migration without outside help?
Yes, if you have Linux, PostgreSQL and identity skills in-house and time to test. Mattermost's documentation covers the Slack import path and the single binary deployment with PostgreSQL. The harder parts are a high availability setup, which needs redundant application servers, database servers and load balancers plus shared file storage on S3, an S3-compatible service or NAS, and the compliance and backup procedures. Outside help is most useful for a fixed-scope hardening, testing and cutover plan, which DeployOpen can document in writing before work starts.
Does Mattermost Team Edition cover our use?
Team Edition fits teams under 250 users that do not need single sign-on, based on Mattermost's editions documentation. It is free, open source and self-hosted under the MIT license for the compiled binaries. If you need SSO, AD/LDAP sync, clustering or compliance export, you need a paid edition, and the Team Edition is not the right baseline. Confirm your user count, your identity requirements and your retention needs against the editions page before you choose the free build.
Which Mattermost edition do we need for SSO and compliance export?
According to Mattermost's pricing page, SSO over SAML, OIDC and OAuth and AD/LDAP user sync are included from the Professional plan. Compliance export is part of the paid Professional, Enterprise and Enterprise Advanced plans, and the free Entry tier has no compliance features. High availability clustering and FIPS 140-3 compliance require Enterprise, and air-gapped deployment requires Enterprise Advanced. Confirm the exact feature list for your target version with Mattermost, because feature placement can change between releases.
What happens to our Slack history on the Free plan?
On Slack's Free plan, you see 90 days of message and file history, and Slack states that content older than one year is permanently deleted. That makes an export before the deletion window the first priority. Every Slack plan can export public channel messages, but private channels and direct messages require a Business+ or Enterprise plan, and that export application must be approved. Work out which history you need to keep before cutover, because deleted Free workspace content cannot be recovered from Slack.
How DeployOpen helps you evaluate and move to Mattermost
DeployOpen is a Chainscore Labs company that plans, implements, hardens, backs up, upgrades and documents self-hosted open-source platforms inside your own cloud accounts, data centers or air-gapped networks. For Slack vs Mattermost, we start by writing down which Slack features your teams depend on and which Mattermost edition covers them, then build and hand over only what the written scope agrees.
How we scope
- We inventory which Slack plan you run and whether private channels and DMs need exporting
- We map your required features, such as SSO, compliance export and huddles, to Mattermost editions
- We agree scope, deliverables and timelines in writing before any build work starts
How we build
- We deploy Mattermost in your environment with PostgreSQL and the file storage your edition needs
- We test a Slack export import in a staging instance and record which items did not move
- We rebuild required integrations and slash commands as Mattermost webhooks, then test them
How we hand over
- We document architecture, configuration, user onboarding and the features left out of scope
- We provide a cutover runbook covering the Slack export window, DNS and user communication
- We train your administrators on upgrades, backups and the monthly Mattermost release cycle
How we support
- Ongoing support, upgrades and continuous testing are available as retainers after handover
- Retainers can cover moving between Mattermost server versions and support windows
- We agree the support scope in writing so your team knows who handles each task
