Open-source alternatives to Microsoft 365

Which open-source alternatives to Microsoft 365 fit your workloads

No single open-source option is a full like-for-like replacement for Microsoft 365. openDesk, Nextcloud with Collabora Online and OX App Suite with Dovecot each cover different parts of the suite, so the practical question is which workloads you can move, in what order, and which ones need a second product. Renewal dates, licensing changes, data residency requirements and lock-in concerns usually trigger this review, and the answer depends on how your organization uses files, documents, mail, calendars and compliance tooling today.

Teams look at alternatives for a few concrete reasons. Exchange Server 2019 is past its extended support, which ended in October 2025 according to the Microsoft Lifecycle page, and Microsoft points customers to Exchange Server SE or Exchange Online. Exchange Server SE follows the Modern Lifecycle Policy with no fixed end date, provided the configuration stays current, so on-premises mail is no longer tied to a fixed support calendar. Nextcloud Hub is licensed under the AGPL and is free to self-host, although Nextcloud GmbH sells enterprise subscriptions for support and extra features. Each of these facts changes the cost and control picture, so record your current Microsoft licensing terms, your Exchange version and your data location requirements before you compare options.

Start with an inventory: list each Microsoft 365 workload, its users, its data volume and any eDiscovery or retention obligations. Map file sync and document editing to Nextcloud with Collabora Online, which edits .docx, .xlsx and .pptx files. Map mail and calendar to OX App Suite with Dovecot, or evaluate openDesk if you want a suite-wide deployment. Confirm with each vendor which features, such as Teams-style chat, meeting tools or advanced compliance holds, are included or missing, because these are the gaps that surface after a pilot.

Which open-source option fits which Microsoft 365 need

Microsoft 365 bundles mail, files, office editing and collaboration into one service, so a replacement is rarely a single product. The options below group those workloads into self-hosted components, and each card names the decision that matters most before you commit to one of them.

openDesk as a full suite

openDesk is an office and collaboration suite built for public administration, managed since January 2024 by ZenDiS, the German federal Centre for Digital Sovereignty. It is deployed to Kubernetes with Helmfile and Helm charts, and the deployment repository is licensed under Apache 2.0. It is offered in a Community and an Enterprise Edition, so check which components each edition includes, who supports the Kubernetes platform beneath it, and whether your team can operate that cluster over the long term.

Nextcloud Hub with Collabora Online

Nextcloud covers files, sharing, calendars and contacts, while Collabora Online supplies browser-based editing for .docx, .xlsx and .pptx files. Collabora Online is licensed under the Mozilla Public License 2.0, and the free CODE edition sits alongside a paid enterprise edition that adds support, SLAs and signed security updates. The trade-off is that you assemble and operate two products, so confirm how office editing performs with your largest documents and how formatting survives round trips with Word and Excel users.

OX App Suite with Dovecot

OX App Suite from Open-Xchange provides email, calendar, documents, drive and tasks, and it can run on premises, in a public cloud or as the managed OX Cloud service. Dovecot is part of the Open-Xchange product line, so mail storage and access can be planned as one stack. This option is the closest match for replacing Exchange mailboxes and Outlook-style calendaring, but you should verify client compatibility for the Outlook and mobile clients your users rely on, and confirm how shared mailboxes and delegation are handled.

Exchange Server SE stays self-hosted

If your organization wants to keep mail on premises with the least change, Exchange Server Subscription Edition is still a self-hosted Microsoft option. It reached general availability on July 1, 2025 and follows the Modern Lifecycle Policy, with no fixed end date while configurations stay current. The trade-off is that you keep Microsoft's licensing and update cadence, and Exchange Server 2019 is no longer a safe choice because its extended support ended in October 2025.

How Microsoft 365 capabilities map to open-source options

This table pairs each core Microsoft 365 workload with the self-hosted open-source options that can cover it, with notes on depth and gaps. Read each row as a starting point for a pilot, and confirm every capability against current vendor documentation before committing to a platform.

Microsoft 365 capability	Open-source option	Coverage notes
Exchange mailboxes	OX App Suite with Dovecot, or openDesk groupware	OX App Suite provides email and calendar and can run on premises. Confirm mailbox migration tooling, protocol support and client compatibility for your Outlook and mobile fleet.
Calendar and contacts	OX App Suite calendar, or Nextcloud calendar and contacts	Covers shared calendars and standard scheduling. Confirm free/busy lookup, room and resource booking, and delegation behavior against your current requirements.
Teams-style chat and meetings	Nextcloud Talk or openDesk components, with a separate video backend where needed	Chat and basic calling are workable for many teams, but large meetings, live transcription and broad device support are areas where you should test and confirm capacity and features.
SharePoint and OneDrive document storage	Nextcloud Hub with desktop and mobile sync	Covers file libraries, sharing links and sync for most document workloads. Confirm version history depth, permission inheritance and site-level structure, since SharePoint team sites do not map one to one.
Word, Excel and PowerPoint editing	Collabora Online, which edits .docx, .xlsx and .pptx	Collabora Online integrates with Nextcloud and other platforms. Test complex macros, pivot tables, tracked changes and advanced formatting with your real documents before rollout.
Purview eDiscovery and retention	Self-hosted audit logging, retention policies and an export process built by your team or partner	This is the widest gap. Open-source platforms do not provide an equivalent of Purview eDiscovery out of the box, so plan for custom legal hold, search and export workflows and confirm them with your legal and compliance teams.
Identity and single sign-on	Keycloak or another OIDC and SAML identity provider, connected to your directory	Standard protocols allow integration with most platforms. Confirm group sync, multi-factor enforcement and provisioning support for each application in your environment.

Why the Microsoft 365 workloads split across several platforms

Microsoft 365 is one license that covers mail, file storage, office editing, calendars and chat, and users experience it as one product. Open-source replacements rarely work that way. A self-hosted equivalent is usually a set of components: a mail server or groupware layer for Exchange and Outlook workloads, a file sync and sharing platform for OneDrive and SharePoint libraries, an office editor for Word, Excel and PowerPoint documents, and a collaboration or calendar layer that ties them together. Each component has its own release cycle, configuration and failure modes, so the first design decision is which components you will run and who owns each one.

The integration points between those components set the shape of the design. For example, Collabora Online is an office editor that is embedded into a file platform such as Nextcloud, so document editing depends on the Nextcloud version, the Collabora version, the WOPI-style connection between them and the reverse proxy that carries it. Each integration point is a place where an upgrade in one component can break another. Ask each vendor or integrator which versions have been tested together, who certifies that combination, and whether the editor and file platform can be upgraded independently. Those answers determine how many support contracts you need and how long a maintenance window will take.

Support and upgrades follow from that split. Under Microsoft 365, one vendor carries the whole stack. In a self-hosted suite, you either buy support from each component vendor or contract a single integrator who takes responsibility for the combined system. Confirm in writing which party patches the mail server, the file platform, the editor and the identity layer, how security fixes reach each one, and who signs off on a version change. Test an upgrade in a non-production copy of the full chain before committing to a schedule, because a suite that is easy to install can still be expensive to keep current.

What a multi-year Microsoft 365 replacement costs by component

This table separates the cost of a Microsoft 365 replacement into its components, marks each as one-time or recurring, and names what moves it up or down. Use it to structure a written comparison against your current subscription, not to estimate totals, since no prices or durations are supplied here. Read the recurring rows first, because they usually decide the multi-year result.

Cost component	Who is paid	One-time or recurring	What drives it up or down
Microsoft 365 subscription and licensing	Microsoft or your reseller	Recurring	Seat count, license tier, add-ons and any E3 or E5 requirement for eDiscovery exports; confirm current terms in your agreement
Infrastructure (compute, storage, backup, network)	Cloud provider or data center vendor	Recurring	User count, mailbox and file volume, retention periods, redundancy level and whether you run an air-gapped or on-premises footprint
Implementation and integration	Implementation partner or internal team	One-time	Scope of workloads (mail, files, documents, identity), identity integration, custom branding and the number of workflows to rebuild
Data migration and eDiscovery export	Implementation partner or internal team	One-time	Volume of mailboxes and SharePoint content, version history depth, document format conversion and validation effort
Support subscriptions (Nextcloud Standard, Premium or Ultimate, Collabora Online enterprise, Open-Xchange support)	Vendors listed in their pricing terms	Recurring	Tier selected, user count, SLA requirements and security update expectations; Nextcloud One managed hosting applies to organizations under 100 users, so ask whether it fits your size
Internal skills and training	Your staff or contractors	Recurring	Team experience with Kubernetes, Linux, mail routing and document servers, plus turnover; training and cross-training reduce dependence on single experts
Security testing and compliance evidence	Testing firm and internal security staff	Recurring	Frequency of testing, scope of applications and APIs, and the evidence your auditor expects; DeployOpen prepares evidence but auditors issue assessments

What you give up when you leave Microsoft 365 and how teams work around it

Moving off Microsoft 365 removes built-in eDiscovery, co-authoring habits, meeting tools, add-ins and vendor-backed SLAs at the same time. Each loss needs a named replacement, an owner and a test before cutover, or it becomes a gap that users discover after go-live.

Legal holds and eDiscovery

Purview eDiscovery bundles search, legal holds and export in one tool that auditors and counsel already know. Self-hosted stacks have no single equivalent, so holds usually move to mailbox and file retention settings, an archive or a documented manual procedure. Confirm which hold scopes you need, who can place them, how they are logged and whether the export format satisfies your legal team before you retire the Microsoft tenant.

Outlook client behavior

Users expect Outlook features such as shared calendars, delegate access, categories and offline cached mailboxes. OX App Suite and Dovecot-based stacks cover core mail and calendar, but Exchange-specific client behavior, such as certain Outlook rules and add-in panes, may not carry over. Pilot with a representative group of users and list every feature they rely on daily before choosing a client.

Co-authoring and format fidelity

Collabora Online opens and edits .docx, .xlsx and .pptx files, but complex layouts, tracked changes, macros, embedded objects and advanced Excel features can render differently from Word or Excel desktop. Test your heaviest documents, such as contracts, financial models and branded templates, in the browser and in desktop clients. Decide in advance whether you will keep Microsoft desktop Office for some roles.

Meetings and chat

Teams combines chat, video meetings, recording and channel-based file storage in one client. Self-hosted replacements typically split these into separate components, such as a chat server, a video conferencing system and a file platform, each with its own administration and user login. Map which meeting and chat features users depend on, including external guest access and recording retention, and confirm each one against the products you select.

Add-ins and Power Platform flows

Microsoft-only add-ins, Office scripts and Power Automate flows often hold business logic that no one has documented. Each one must be inventoried, rewritten against a new integration method or retired. Start with an export of active flows and add-in usage from your administration centers, then assign an owner for each item so workflows do not silently stop when the tenant is switched off.

Vendor SLAs become a support contract

Microsoft 365 comes with contractual uptime commitments and a support channel that you do not have to design yourself. A self-hosted suite replaces those with the support terms of whichever vendor or integrator you sign, such as a paid Collabora Online enterprise subscription, Nextcloud Enterprise or a services contract. Ask for written response times, patching commitments, escalation paths and who is accountable for backups and restores.

How to move mailboxes and SharePoint content out of Microsoft 365

This sequence moves mailboxes and SharePoint or OneDrive content into a self-hosted platform in controlled waves, with retention evidence kept and users switched over only after a pilot has passed. The output is a verified copy of the data, a tested cutover, and a decommission record that an auditor or legal team can follow.

Inventory workloads and retention obligations
List every mailbox, SharePoint site, OneDrive account and Teams-linked library in scope, then record which of them sit under legal holds, retention labels or regulatory retention periods. Ask legal, records management and compliance owners to confirm the obligations in writing, because these decide what must be exported and what must stay available after cutover. The step is done when each workload has an owner, a retention requirement and a target platform, such as OX App Suite with Dovecot for mail or Nextcloud with Collabora Online for files.
Confirm eDiscovery export licensing and access
Verify that the accounts performing exports hold a Microsoft 365 E3 or E5 license, since Microsoft Learn states that exporting requires one of these. Confirm which administrators can create eDiscovery cases and who approves them. Check the license position with Microsoft or your reseller before the project starts, because a gap here blocks the whole export. The step is complete when named operators have confirmed access and the license basis is recorded.
Export mailboxes and SharePoint content through Purview
Create an eDiscovery case, run searches scoped to each inventoried workload, and export results. Mailbox items come out as PST or .msg files, while SharePoint and OneDrive content comes out as native documents, and you should select version history where your retention rules require it. Search export packages expire 14 days after creation, so download and checksum each package promptly and plan the export batches around that window. The step is done when every package is downloaded, its hash is logged, and the item counts match the search reports.
Map permissions, folders and metadata
Translate Microsoft 365 sharing rights, group memberships and site hierarchies into the target platform's model, such as Nextcloud groups, shares and folder permissions, or the mailbox and delegation structure in OX App Suite. Document where a permission cannot be expressed one-to-one and decide the compensating control. Note that Office files will open in Collabora Online, but co-authoring and feature parity need to be tested with real documents. The step closes when a signed permissions map exists and each exception has a named decision owner.
Import and pilot with a user group
Import the exported data into the target environment and move a small, representative user group onto it first. Give the pilot group a clear list of what changes, including new sign-in paths, sync clients, sharing links and document editing behavior. Collect defects for a set period agreed in advance, and fix import mapping problems before widening scope. The step is complete when the pilot group has signed off, open defects are closed or accepted, and the import process is repeatable.
Run in parallel and reconcile
Keep Microsoft 365 and the target platform available side by side while new mail and file changes are synchronized or re-exported for the remaining users. Reconcile item counts, folder structures and version histories against the export records on a fixed schedule. Keep the source tenant under its existing retention holds during this period. The step is done when reconciliation reports show no unexplained differences for each workload.
Cut over DNS, client profiles and sign-in
Change the MX, autodiscover and other mail DNS records, update mobile and desktop client profiles, and switch sign-in and sync endpoints for each user group in turn. Confirm mail flow in both directions, calendar free/busy behavior, and that the sync client connects to the new service without data loss. Ask your network and identity teams to confirm DNS change windows and rollback steps before the first switch. The step is complete when every group has passed a post-cutover check and rollback has been tested.
Decommission and retain evidence
Once retention obligations are met and the legal team has released holds, remove licenses, disable accounts and shut down the Microsoft 365 workloads in the agreed order. Keep the eDiscovery exports, checksums, reconciliation reports and approvals in an archive that meets your retention rules, since these records support any later audit. The step is done when the decommission checklist is signed, the evidence archive is verified, and the remaining retention obligations have an owner.

Which Microsoft 365 replacement fits your situation

Choose this path when regulators, customer contracts or internal policy require mail, files and documents to stay in a named region or inside your own data center or air-gapped network. A self-hosted stack such as Nextcloud Hub with Collabora Online for documents, or OX App Suite with Dovecot for mail, runs inside infrastructure you control, so the location of every copy is a decision you document rather than a term you negotiate.

Hosting boundary: Confirm which services leave your network, including search indexing, push notifications, mobile sync relays and any vendor telemetry.
Backups and replicas: Decide where backups, snapshots and disaster recovery copies live, since they often fall under the same residency rule.
Air-gapped operation: Ask each vendor whether updates, license checks and document previews work without internet access.
Mail and file scope: Mailboxes, shared drives and chat history may need separate residency decisions.
Operations staff access: Map which administrators in other countries can reach the systems and logs.

Before committing, ask your data protection or compliance lead to confirm the residency rule in writing, and ask DeployOpen or another implementer for a scoped plan that names each component and its location.

What buyers ask before replacing Microsoft 365

How much effort does replacing Microsoft 365 actually take?

Effort depends mostly on how many workloads move, how much data and history each one holds, and how many integrations depend on Microsoft services. Mail, calendar and contacts, file sync, document editing, and team sites each carry separate work: mailbox migration, identity and client changes, format conversion, permission mapping and user retraining. Each workload has its own one-time migration cost and recurring operating cost, and the recurring part grows with user count, storage and the number of services you run. Ask any partner to break the estimate down by workload, and to state which items are one-time and which recur.

Can our internal team run this migration without an outside partner?

Some organizations can, especially where they already operate Linux, Kubernetes or identity platforms and have staff who have migrated mail before. The questions to answer honestly are whether anyone has run a directory-backed mail platform in production, who owns backups and upgrades after cutover, and whether the team can absorb the migration alongside normal work. DeployOpen plans, implements, integrates, hardens, backs up, upgrades and documents self-hosted platforms inside your own infrastructure, and most engagements are fixed-scope with deliverables agreed in writing before work starts. Ongoing support and upgrades are available as retainers.

How long does a migration off Microsoft 365 take?

No general duration applies, because timing is set by data volume, the number of users, how many workloads move in each wave, and how much coexistence you need during the transition. Mailboxes and file libraries with long version histories take longer to transfer and validate than small, recently created sites. Plan for a period where both platforms run side by side, and schedule cutover around business calendars and change freezes. A written scope should list waves, the acceptance criteria for each wave, and the dependencies on your identity provider. Ask for the timeline as a set of milestones rather than a single date.

What does the migration need from our IT and security teams?

Expect demands in four areas: identity (directory design, single sign-on, and account mapping), infrastructure (hosting, storage, backup targets and network paths), security (certificates, mail routing, DNS records, and access policy), and change management (client reconfiguration, user support and training). Your security team should review where data is stored, who holds administrative access, and how logs are kept. Compliance readiness work can prepare systems, controls and evidence for an assessment, but independent auditors and certification bodies issue any report or attestation. Confirm your own control obligations before the scope is written.

Can Purview eDiscovery exports be replaced, and what should we confirm?

Purview eDiscovery exports Exchange mailbox items as PST or .msg files and SharePoint and OneDrive content as native documents with selectable version history, according to Microsoft Learn. Those export packages expire 14 days after creation, and exporting requires a Microsoft 365 E3 or E5 license. Before you cut over, confirm with counsel and your records team which holds, retention rules and legal requirements apply, and whether the exported PST files and version histories meet them. Your replacement needs its own retention and legal-hold process, and you should test that restored items are complete and searchable. Do not treat a bulk export as a substitute for a documented retention policy.

How do we compare a quote against a fixed written scope?

Compare quotes against the same written scope, not against each other's headline total. A fixed-scope agreement should list the workloads, the number of mailboxes and file libraries, integrations, the acceptance tests for each deliverable, documentation and handover, backup and upgrade responsibilities, and the assumptions that would change the price. Ask which items are one-time, which are recurring (support, upgrades, continuous testing), and what happens if the data volume or user count differs from the assumptions. DeployOpen does not publish a price list, and a quote follows from the written scope. Ask every vendor for the same scope document before comparing numbers.

What changes for users after the move

The biggest user-facing change is sign-in. Today most staff authenticate to Microsoft 365 through Entra ID, often with conditional access and multifactor prompts they already recognize. After the move, the identity provider is whatever you connect to the suite, so decide before the pilot whether accounts come from an existing directory through LDAP or OIDC, and whether single sign-on and multifactor are enforced at the identity layer or in each application. Users will see a new login page, possibly a new password flow, and different session timeouts. Confirm with your identity team how these prompts behave in each component, because a user who signs into the mail client and the document editor separately will generate a support ticket on day one.

Clients and file links change more than most teams expect. Outlook, Word, Excel and PowerPoint desktop apps will be replaced by web clients or by whatever desktop mail and office clients the chosen suite supports, and each of those has its own settings, shortcuts and offline behavior. Links to documents will point to a new host, so existing bookmarks, SharePoint URLs in email and links embedded in other systems will need a redirect plan or a communication to owners. Co-authoring also needs checking: Collabora Online edits ODF and Microsoft formats including .docx, .xlsx and .pptx, but layout, macros, tracked changes and comments can render differently from Word, so run a pilot with the documents your finance and legal teams actually use. Calendar sharing, free/busy lookup and meeting invitations across organizations are another area to test, because they depend on the mail backend and on the calendar protocols your mail client supports. Ask the vendor or integrator to document which of these features work and which need a workaround.

Mobile apps are the final area. Device management, app store distribution and the mail profile on each phone all need to be rebuilt for the new platform, and any existing Intune or mobile device policy will not carry over automatically. Prepare training around the tasks people do every day, such as sending a shared file, finding a meeting room and recovering a deleted document, rather than around product features. Select a pilot group that includes heavy co-authors, an executive assistant, a mobile-only user and someone in a regulated function. Run the pilot for long enough to cover a month-end cycle, collect tickets by category, and agree exit criteria in writing before the wider rollout starts.

How DeployOpen scopes, migrates, hands over and supports the replacement

DeployOpen plans, implements, customizes, integrates, hardens, backs up, upgrades, documents and supports self-hosted open-source platforms inside your own cloud accounts, data centers or air-gapped networks. For a Microsoft 365 replacement, that means working through the written scope for each workload before any mailbox or site is moved.

How we scope

Inventory which Microsoft 365 workloads are in use, including Exchange mail, SharePoint sites, OneDrive files and Teams chat.
Agree in writing which workloads move, which stay, and which are retired, with deliverables and timelines set before work starts.
Confirm your Purview eDiscovery licensing and export needs, since exporting requires an E3 or E5 license under current Microsoft terms.

How we build

Deploy the agreed platforms, such as Nextcloud with Collabora Online or openDesk, into your own infrastructure with documented configuration.
Integrate identity, mail routing and document editing so users reach the replacement services through their existing sign-in.
Test file format fidelity for .docx, .xlsx and .pptx files, and verify sharing and permissions before user data is moved.

How we hand over

Provide written runbooks covering installation, configuration, backup, upgrade and restore procedures for your operations team.
Deliver migration records showing what was exported from Microsoft 365, when, and how each set of content was verified.
Prepare user guidance that explains changes in editing, sharing links and mail clients, so support desks receive the same information.

How we support

Offer ongoing support, upgrades and continuous security testing as retainers after cutover, scoped separately from the migration.
Keep the platform current with planned upgrades, documented against the versions you run in your own environment.
Prepare controls and evidence for compliance assessments, while independent auditors and certification bodies issue any reports or attestations.