Which self-hosted team chat fits your situation
If you are building a Slack or Teams replacement shortlist, start with the operating model you can support, not the feature grid. Mattermost fits teams that want a single Linux binary backed by PostgreSQL, with SSO and high availability on paid tiers. Rocket.Chat fits teams that want a MongoDB-backed platform, a free Starter tier for up to 50 users, and are willing to separate the MIT core from enterprise code they may need to license. Matrix, usually through the Synapse homeserver, fits organizations that need federation with other servers and bridges to other networks. Zulip fits teams whose main problem is keeping many parallel discussions readable through topic threading. No option is universally better, and licensing and paid tiers differ materially between them.
Confirm the features you truly need before you compare prices. For Mattermost, SSO (SAML, OIDC, OAuth) and AD/LDAP sync start at the Professional plan, while high availability needs Enterprise, and HA requires shared file storage such as S3, an S3-compatible service or NAS on every node. For Rocket.Chat, check whether LDAP group mapping, MFA, audit trails and automated failover are on your required list, since several sit in paid plans. For Synapse, SSO runs through OpenID Connect, SAML2 or CAS in its configuration, and federation is controlled by settings such as federation_domain_whitelist. Ask each vendor, or your own platform team, to confirm these items against the current plan documentation.
Plan the upgrade cadence before you commit. Mattermost ships server binaries monthly and labels some releases as Extended Support Releases with longer windows. Rocket.Chat standard releases are supported for 6 months and LTS releases for 12 months, and unsupported versions can lose connection to the official mobile and desktop clients. Synapse upgrades can be hard to roll back because of schema changes, so test each upgrade in a staging environment first. Our Mattermost and Rocket.Chat references are the natural next reads for these support windows.
How each option fits a team's situation
A small team with a modest user count often starts on a free tier, and the question is whether the free edition covers the features the team will need in a year, not only today. Rocket.Chat's free Starter plan allows up to 50 users and includes LDAP and Active Directory authentication, single sign-on, multi-factor authentication, end-to-end encryption, retention and read receipts, which makes it a strong fit when headcount stays under that cap. Mattermost's free tier is not the focus here, so confirm current free-tier limits directly with the vendor before you commit.
- Rocket.Chat Starter ceiling: the 50-user limit on Starter is the trigger that moves you to a paid plan, and the paid plans are priced by quote.
- Rocket.Chat Community workspace: the free Community workspace allows up to 100 concurrent users with core messaging, but it does not carry the Starter feature set.
- Matrix with Synapse: Synapse is AGPL-3.0 and runs without a license fee, but a small team still needs to run PostgreSQL in production and keep up with releases.
- Upgrade discipline: Rocket.Chat standard releases are supported for 6 months and LTS releases for 12 months, so a small team must plan regular upgrades to keep clients working.
- Hidden time cost: the cost of a free platform is staff time for hosting, backups and upgrades.
Confirm the user ceiling, the feature list for your edition and the upgrade cadence you can sustain before you pick a free tier.
A regulated enterprise usually needs identity integration, retention controls and audit evidence before it needs a low hosting cost. In this situation the paid edition question matters most, because several controls sit behind paid plans. Mattermost's pricing page places SSO (SAML, OIDC, OAuth) and AD/LDAP user sync from the Professional plan, high availability clustering and FIPS 140-3 compliance from Enterprise, and air-gapped deployment in Enterprise Advanced. Rocket.Chat's paid plans list LDAP and SAML user group mapping, tamper-evident audit trails of messages, files and sessions, and built-in redundancy with automated failover.
- Identity and sessions: SSO and directory sync are the first controls to verify in the edition you buy, not in a higher tier.
- Audit trails: Rocket.Chat lists tamper-evident audit trails on paid plans, so confirm whether your evidence requirement needs that feature.
- High availability cost: Mattermost high availability is available only on Enterprise and Enterprise Advanced and needs shared storage on S3, an S3-compatible service or NAS mounted on each node.
- Air-gapped operation: air-gapped deployment is a paid-plan capability on both platforms, so it belongs in the quote.
- Compliance mapping: DeployOpen prepares systems and evidence for assessments, but independent auditors issue any attestation.
Ask each vendor for the edition that includes your required controls in writing, then check it against your control set.
Federation matters when users in different organizations must talk to each other without sharing one tenant. Matrix is the option built around this model, and Synapse is the most widely documented homeserver. Synapse federates on port 8448 by default, and delegation lets user IDs such as @user:example.com be served from another host on port 443, so the server_name setting must be planned before the first user joins. Federation is controlled by the federation_domain_whitelist setting, where an empty list disables federation entirely.
- Federation control: the federation_domain_whitelist setting limits traffic to listed domains, and the docs recommend firewalling the federation listener as well.
- Identity linkage: Synapse supports OpenID Connect, SAML2 and CAS, so partner-organization sign-in can be wired to existing identity providers.
- Licensing: Synapse is AGPL-3.0 with commercial licenses available from Element, which matters if you modify and host it for others.
- Rollback risk: the Synapse upgrade notes warn that rolling back can be difficult because of database schema changes between releases.
- Scale path: workers and Redis are the scaling route for busy federated deployments.
Confirm your federation partners, domain naming and licensing position before you deploy a homeserver.
Engineering teams that run many parallel discussions often find flat channel chat hard to follow. Zulip is the option covered for topic-threaded chat, and the comparison here is about whether threading structure matters more than a Slack-style channel model. Zulip's topic-based threading is its defining design, and this page covers it as the threading-first alternative, so confirm its current plans and hosting details on its own comparison page before you decide.
- Threading as the core model: topics keep discussions on one question together, which helps teams that work across incidents and code reviews.
- Channel-first alternatives: Mattermost and Rocket.Chat use channel and thread structures that suit teams already fluent in Slack or Teams.
- Integration effort: a chat platform that engineers use daily needs bots, webhooks and CI notifications, so check integration support for your toolchain.
- Mobile and client support: Rocket.Chat warns that unsupported versions may lose connection to official mobile and desktop clients, so client compatibility is part of the upgrade plan.
- Migration: Rocket.Chat supports Slack exports, while Mattermost data moves into Rocket.Chat through CSV conversion.
Run a two-week pilot with a real backlog of threads and check whether topic structure reduces noise for your team.
Which team chat option fits which scenario
This table maps common team chat situations to the platform that fits best, with the condition that makes each fit hold. Read the third column before the second, because the conditions and paid plan requirements often decide the choice.
| Scenario | Best fit | Why and the condition that matters |
|---|---|---|
| Free-tier pilot with a small team | Rocket.Chat Starter or Mattermost Free | Rocket.Chat's free Starter plan allows up to 50 users and includes LDAP, AD, SSO and MFA, so it suits a small pilot. Confirm current Mattermost free-tier limits on its pricing page before committing. |
| SSO and AD sync on a paid plan | Mattermost Professional or Rocket.Chat paid plans | Mattermost includes SSO (SAML, OIDC, OAuth) and AD/LDAP sync from Professional. Rocket.Chat lists LDAP and SAML group mapping on paid plans. Get written confirmation of which features each tier includes. |
| Air-gapped deployment | Mattermost Enterprise Advanced or Rocket.Chat paid plan | Air-gapped deployment is a paid capability on both platforms. Rocket.Chat states it is not available on Starter. Confirm the exact tier and offline update process in writing before procurement. |
| Federation with external organizations | Matrix with Synapse | Synapse federates by default on port 8448 and can be restricted with a domain allowlist. Mattermost and Rocket.Chat are better fits when external federation is not required, because they do not offer the same open federation model. |
| Topic-threaded engineering chat | Zulip, or Matrix if federation matters | Zulip is covered separately for topic-based threads that suit engineering discussions. Choose Matrix only when cross-organization federation is a requirement, since its threading model differs. |
| Migrating from Slack | Mattermost or Rocket.Chat | Rocket.Chat imports full Slack workspace exports and Slack users from CSV. Mattermost has a documented Slack migration guide. Test the import with a copy of real data and confirm which history, files and user mappings survive. |
What the license and paid tiers actually gate
Start with the license, because it decides what you can build on and what you pay for. Mattermost licenses its compiled binaries under MIT, releases its source for custom builds under AGPL v3.0, and offers a commercial alternative from Mattermost, Inc. for teams that cannot accept AGPL terms. Its paid tiers are Professional, Enterprise and Enterprise Advanced, sold as prepaid annual subscriptions by seat count. SSO (SAML, OIDC, OAuth) and AD/LDAP user sync start at Professional, high availability clustering and FIPS 140-3 compliance start at Enterprise, and air-gapped deployment sits in Enterprise Advanced. The pricing page lists no public prices, so every figure has to come from a quote tied to your seat count and tier.
Rocket.Chat keeps its core under MIT, but code in the apps/meteor/ee and ee directories falls under a separate enterprise license, so the boundary is in the repository itself. The free Starter plan includes LDAP and Active Directory authentication, single sign-on, multi-factor authentication, end-to-end encryption and retention, up to 50 users. Air-gapped deployment, multi-instance and microservice designs, SAML user group mapping, tamper-evident audit trails and automated failover are paid capabilities, and pricing is by quote under the Commercial, Government and Defense plans. Ask the vendor to show, in writing, which of your required controls appear in the plan document you are buying. Synapse, the Matrix homeserver from Element, is AGPL-3.0-or-later, and Element sells commercial exceptions for organizations that cannot meet AGPL obligations. Zulip is Apache-2.0. For Matrix and Zulip, confirm per distribution which admin, compliance and client features ship with the server and which come from a hosted, bundled or vendor-supported edition, since the license text alone does not answer that.
Capability comparison across self-hosted chat options
This table compares licensing, database, free tiers, identity, high availability, compliance, federation, mobile clients and Slack migration across four chat platforms. Where a supplied fact does not cover a cell, the cell says to confirm with the vendor, so treat those gaps as checklist items for your quote and proof of concept.
| Capability | Mattermost | Rocket.Chat | Matrix (Synapse) | Zulip |
|---|---|---|---|---|
| License | MIT for compiled binaries, AGPL v3.0 for custom build source, commercial alternative available | MIT core; enterprise directories under a separate Rocket.Chat license | AGPL-3.0-or-later for Synapse; Element sells commercial exceptions | Apache-2.0 team chat; confirm current edition terms with vendor |
| Database | PostgreSQL | MongoDB 8.0 or later as a replica set | PostgreSQL recommended for production; SQLite supported | Confirm with vendor |
| Free tier | Paid plans only in supplied facts; confirm any free tier limits with vendor | Starter free up to 50 users; Community workspace up to 100 concurrent users | Open-source server with no seat fee in supplied facts; confirm Synapse Pro terms | Confirm with vendor |
| SSO and directory sync | SAML, OIDC and OAuth SSO plus AD/LDAP sync from the Professional plan | LDAP, Active Directory and SSO on Starter; SAML group mapping on paid plans | OIDC, SAML2 and CAS SSO; confirm directory sync options | Confirm with vendor |
| High availability | Enterprise and Enterprise Advanced only; needs shared S3, S3-compatible or NAS storage on each node | Three-member MongoDB replica set recommended; multi-instance designs need a paid plan | Scales through workers and Redis; confirm your own high availability design | Confirm with vendor |
| Compliance and retention | FIPS 140-3 compliance from Enterprise; confirm retention and audit features | Retention and end-to-end encryption on Starter; tamper-evident audit trails on paid plans | Confirm retention and audit options in Element documentation | Confirm with vendor |
| Federation | Confirm with vendor | Confirm with vendor | Federates on port 8448 by default; can be limited by domain allowlist or disabled | Confirm with vendor |
| Mobile push and clients | Confirm mobile push setup with vendor | Unsupported versions may lose official mobile and desktop client connectivity | Uses Matrix clients; confirm push gateway setup | Confirm with vendor |
| Slack migration path | Documented migrate-from-Slack guide; confirm import scope with vendor | Imports full Slack workspace exports and Slack users from CSV | No Slack import tool in supplied facts; confirm with vendor or bridge options | Confirm with vendor |
Each option in brief, with its license
Mattermost, Rocket.Chat, Synapse and Zulip each take a different route to self-hosted chat, and their licenses differ in ways that change what you pay for. Read each card for the license, the paid model and the condition under which that option fits your team.
Mattermost
Mattermost is an open core platform that runs as a single Linux binary on PostgreSQL. Compiled binaries are MIT licensed, custom builds fall under AGPL v3.0, and Mattermost, Inc. sells a commercial alternative for teams that cannot take on AGPL terms. SSO and AD/LDAP sync start at the Professional plan, while high availability needs Enterprise and shared file storage on S3, an S3-compatible service or NAS. Check which plan carries the controls you need before you commit.
Rocket.Chat
Rocket.Chat is maintained by Rocket.Chat Technologies Corp. Its core is MIT licensed, but the apps/meteor/ee and ee directories sit under a separate Rocket.Chat enterprise license, so enterprise code is not open source in the OSI sense. The free Starter plan covers up to 50 users with SSO and MFA, while air-gapped deployment and multi-instance designs need a paid plan. It requires MongoDB as a replica set and needs regular upgrades to keep mobile and desktop clients working.
Synapse (Matrix)
Synapse is the most widely documented Matrix homeserver, developed by Element and distributed under AGPL-3.0, with commercial licenses also available from Element. Since December 13, 2023, its future contributions are AGPLv3 rather than Apache 2.0, and contributors sign a CLA. It federates by default and scales through worker processes coordinated by Redis. Choose it when federation with other Matrix servers matters, and confirm how your team will run PostgreSQL and rollbacks, since upgrades can change the database schema.
Zulip
Zulip is an Apache-2.0 team chat that organizes conversations into topics within streams, which suits teams that need threaded context across long-running discussions. The self-hosted server is free under Apache-2.0, and paid self-hosted plans and Zulip Cloud are offered by the vendor. Choose it when your main problem is conversation sprawl rather than a Slack migration with many integrations. Confirm the current edition terms, SSO options and mobile push setup directly with the vendor before you plan rollout.
How SSO, retention and audit differ across the options
The first decision is which identity controls you need on day one, because the options gate them differently. Mattermost includes SSO over SAML, OIDC and OAuth plus AD/LDAP user sync from its Professional plan, so you pay for a subscription before those controls are available. Rocket.Chat's free Starter plan includes LDAP and Active Directory authentication, single sign-on and multi-factor authentication, but SAML user group mapping and tamper-evident audit trails of messages, files and sessions sit in the paid plans. Synapse has no paid gate on identity: its configuration manual documents oidc_providers, SAML2 through saml2_config and CAS, so the work moves to your team, which must wire the identity provider, attribute mapping and account lifecycle itself.
Retention and audit need the same scrutiny. Rocket.Chat lists retention on Starter, while its audit trail is a paid capability, so confirm which retention and export features your chosen tier covers before you write a policy around them. For Mattermost, confirm in its pricing and documentation which retention and audit features belong to each plan. For Synapse, retention and audit logging are configured and operated by you, so the policy, log storage, log integrity and access review all become your responsibility. Ask each vendor, in writing, which controls are in each edition and which are roadmap items.
Compliance claims need a confirmed control set before anyone promises them. Name the framework, the controls it requires and the evidence each control produces, then map each one to a feature in the tier you are buying, including how SSO sessions, MFA enforcement and log retention are configured. DeployOpen can plan the configuration, document it and prepare evidence for an assessment, but it does not issue audit reports, attestations or certifications; an independent auditor or certification body does that. Treat an unconfirmed control as an open item in the quote scope, not as something the platform already provides.
How to choose and pilot a chat platform
This sequence turns a shortlist of Mattermost, Rocket.Chat, Matrix and Zulip into a scoped decision, a tested pilot and a written quote that your security, compliance and platform teams can sign off on.
Define user count and federation needs
Start by writing down the number of named users, the number of guest or external users, and whether you must talk to people on other organizations' servers. Federation matters most for Matrix, where Synapse can restrict federation to listed domains with the federation_domain_whitelist setting and an empty list disables it. Mattermost and Rocket.Chat are closed by default for cross-organization chat, so confirm that requirement with your legal and security owners. The step is done when the requirement sheet names a user ceiling, a federation yes or no, and the owners who signed it.
Confirm license and paid tier for SSO and HA
Map each required control to the edition that includes it. Check the current vendor pricing and plan pages for SSO, LDAP or Active Directory sync, multi-factor authentication, retention, audit trails, high availability and air-gapped deployment, because these sit in different paid tiers on each platform. Mattermost lists SSO and AD/LDAP sync from its Professional plan and high availability from Enterprise, while Rocket.Chat lists SSO and LDAP on its free Starter plan but places multi-instance designs and air-gapped deployment on paid plans. Ask each vendor to confirm these placements in writing. The step is done when every must-have control has a named edition and a vendor confirmation.
Size the database tier for each platform
Size the data layer before you choose hardware. Mattermost runs on PostgreSQL, and its high availability cluster needs shared file storage such as S3, an S3-compatible service or NAS on every node, because local storage risks file corruption. Rocket.Chat 8.x requires MongoDB 8.0 or later as a replica set, with three members strongly recommended for high availability. Synapse recommends PostgreSQL 14 or newer for current releases and scales through workers connected to Redis. Your platform team should produce a sizing note with backup, restore and replica design for the chosen database. The step is done when the note is reviewed by your database owner and the replication and backup approach is agreed.
Run a pilot with a Slack export test
Run a pilot in a non-production environment with a representative set of channels, users and integrations. Export a real Slack workspace or a sample that matches its structure, then test the import path for each shortlisted platform. Rocket.Chat supports full Slack workspace exports and a CSV importer, while Mattermost documents its own Slack migration path. Check that users, channels, direct messages, attachments and permissions arrive correctly, and that SSO login, mobile push and retention behave as your policy requires. The step is done when a written pilot report lists what migrated cleanly, what needed manual work and which controls were tested.
Check upgrade cadence against support windows
Compare each platform's release cadence with your ability to upgrade. Mattermost releases server binaries on the 16th of each month and publishes Extended Support Release lines, so confirm which line your organization will run and its end-of-support date. Rocket.Chat supports standard releases for 6 months and LTS releases for 12 months, and unsupported versions can lose connection to official mobile and desktop clients. Synapse warns that rolling back can be difficult because of schema changes between releases. Write a patch and upgrade calendar with a named owner for each platform. The step is done when the calendar shows how each candidate would be kept inside a supported version.
Request a written scope and quote
Once the requirements, sizing, pilot results and upgrade plan are settled, ask the vendor and the implementation partner for written proposals against the same scope. Vendor prices are quote-based on most of these platforms, so ask for seat counts, edition, support tier, high availability components and renewal terms in writing. DeployOpen plans, implements, integrates, hardens, backs up, upgrades and documents self-hosted platforms in your infrastructure, and most engagements are fixed-scope with deliverables and timelines agreed before work starts. Ask for a quote that separates one-time setup from recurring license, support and upgrade work. The step is done when you hold a signed scope that matches the requirement sheet.
Questions buyers ask before hiring help with self-hosted chat
What drives the cost of running self-hosted team chat?
Cost is driven mostly by who runs the platform, how many users and concurrent connections it carries, and which paid tier you need for features such as SSO group mapping, high availability or air-gapped deployment. Mattermost sells Professional, Enterprise and Enterprise Advanced plans as prepaid annual subscriptions by seat count, and its pricing page lists no public prices. Rocket.Chat prices its Commercial, Government and Defense plans by quote. Recurring costs include subscriptions or support, infrastructure, database and storage operations, and upgrade labor. Ask each vendor for a quote that lists the tier, seat or user count, support terms and any features your compliance team requires.
Can our team run self-hosted chat without outside help?
A team with Linux, database and identity administration skills can run a single-node deployment, but the work grows with scale and compliance demands. Mattermost runs as a single Linux binary with PostgreSQL, while Rocket.Chat 8.x requires MongoDB 8.0 or later as a replica set. Matrix homeservers such as Synapse add Redis when scaled with workers. Ask whether your staff has time for monthly upgrades, since Rocket.Chat standard releases are supported for 6 months and LTS releases for 12 months. Outside help is most useful for scoping the architecture, hardening, migration and recurring upgrades, and DeployOpen delivers these as fixed-scope work or retainers.
How long does a pilot take and what does it need from staff?
The length of a pilot depends on the number of channels to test, identity integration, the number of pilot users and how much custom work is needed. No duration is fixed by the vendors' published material, so ask for a written timeline in the scope before work starts. Staff typically need to provide an identity provider test tenant, a Linux host or cluster target, a database owner, a named business owner for acceptance and access to a few representative users. Confirm with the vendor which SSO protocols and mobile push options your pilot must prove, because these shape the test plan.
What does a Slack or Teams migration involve?
A migration involves exporting history, mapping users and channels, and testing whether the imported data is usable for your retention and search requirements. Rocket.Chat supports full Slack workspace exports, Slack users from CSV and a CSV importer for other sources. Mattermost publishes a guide for migrating from Slack, and Mattermost data moves into Rocket.Chat by converting its export into CSV. Teams exports need separate handling, so confirm what format and scope you can obtain. Ask any provider to state which content types (messages, files, reactions, threads) are carried across and which must be rebuilt.
What does high availability require in storage and database?
High availability requires redundant application servers, redundant database servers and shared storage that every node can reach. Mattermost high availability is available only on its Enterprise and Enterprise Advanced plans, and its cluster needs shared file storage on Amazon S3, an S3-compatible service or a NAS mounted on each node, since local file system storage risks corrupting files. Rocket.Chat recommends a three-member MongoDB replica set for high availability, and its paid plans include built-in redundancy with automated failover. Confirm with each vendor which database topology, load balancer and file backend are supported in your environment before budgeting.
How do upgrade cadence and support windows change the work?
Upgrade cadence sets how often your team or your provider must test and deploy new versions, and missed windows can remove features. Mattermost releases server versions in binary form on the 16th of each month, and its Extended Support Releases differ from standard releases in support length. Rocket.Chat warns that after end of life a version gets no security or bug fixes, and that cloud services and mobile client connections may stop working. Synapse notes that rolling back can be difficult because of schema changes between releases. Plan for a recurring test environment, a documented rollback path and a named owner for each upgrade.
What should a quote for self-hosted chat include?
A useful quote lists the scope, deliverables, environment assumptions and exclusions in writing before work starts. Ask for the platform tier and license terms, the number of users or seats, the target hosting topology, the identity integrations, the migration sources and volume, the compliance evidence you expect, and the support and upgrade terms. Separate one-time work such as design, deployment and migration from recurring work such as upgrades, monitoring and testing retainers. Confirm which subscription fees are paid to the vendor and which are paid to the implementation partner, and ask for the assumptions that would change the price.
How DeployOpen scopes and supports a chat selection
DeployOpen is a Chainscore Labs company that plans, implements, integrates, hardens, documents and supports self-hosted open-source platforms inside the client's own infrastructure. For a team chat decision, the work starts with a written scope that fits the platform you choose, whether that is Mattermost, Rocket.Chat, Matrix or Zulip.
How we scope
- Confirm which chat platform and edition fit your user count, identity provider and compliance needs before work begins.
- Record the target infrastructure, whether cloud accounts, data centers or air-gapped networks, in the written scope.
- Agree deliverables, timelines and exclusions in writing, since most engagements are fixed-scope.
How we build
- Plan the database, file storage and clustering design the chosen platform requires, such as PostgreSQL, MongoDB replica sets or Synapse workers.
- Configure SSO, directory sync, retention settings and mobile client access against your identity and policy requirements.
- Test the deployment against the agreed scope and document the configuration, including upgrade and rollback steps.
How we hand over
- Deliver runbooks covering installation, backup, restore and the upgrade cadence of the chosen platform.
- Document integration points, admin roles and any licensed components so your team can operate the platform.
- Provide evidence of controls and configuration that your internal or external assessors can review.
How we support
- Offer ongoing support, upgrades and continuous testing as a retainer, separate from the initial fixed-scope work.
- Plan upgrades around the vendor's release and support windows so the platform stays inside its supported versions.
- Ask any quote to itemize implementation, testing, documentation and retainer work so you can compare options clearly.
