Exchange 2016 and 2019 end of support: self-hosted options

Exchange Server 2016 and 2019 end of support: what your options are

Exchange Server 2019 extended support ended in October 2025, and Microsoft points customers still on it to Exchange Server Subscription Edition or Exchange Online. If your estate runs Exchange 2016 or 2019, mail, calendars and legal retention now depend on a platform that no longer receives standard security fixes from Microsoft, so the question is which path you take and by when. Confirm the Exchange 2016 end date on the Exchange Server 2019 lifecycle page and in Microsoft's lifecycle listings for 2016, because your risk register and board paper should cite the vendor's own dates.

The short answer is that a self-hosted path is viable. OX App Suite and grommunio can both replace on-premises Exchange, but each needs a migration plan with a fixed deadline, a named owner and a cutover window agreed before any mailbox moves. Subscription Edition keeps you on Exchange but brings subscription or Software Assurance licensing for servers and every client access license, so compare its recurring cost with the one-time and recurring costs of an open-source platform. Ask your Microsoft partner to quote Subscription Edition in writing, and ask any open-source provider for a scope that lists mailbox counts, client types and retention requirements.

Start with an inventory: mailbox count, shared and resource mailboxes, archives, journaling and litigation holds, mobile and Outlook client versions, and every system that relays mail through Exchange. Those facts decide which self-hosted platform fits and how long the migration takes. Confirm with your legal and compliance teams which retention and eDiscovery obligations must survive the move, because a self-hosted server will not inherit Exchange's hold and export tooling by default. Illustratively, an estate with a few thousand mailboxes and several archive stores will need far more testing time than a small office with one domain.

What a post-support mail platform has to meet

Exchange Server 2016 and 2019 are past their support windows, so any replacement has to be supported, runnable by your team, and fit your directory and clients. The four to six requirements below connect the platform choice to the decisions you must make before a cutover deadline.

A supported release with a known cadence

Check how long each release stays supported before you commit. Open-Xchange publishes a support commitment in which a standard release is supported for 12 weeks, ending with the third following release, and an LTS release is supported until the next LTS plus six months. Exchange Server SE follows the Modern Lifecycle Policy, so its support depends on keeping configurations current. Ask each vendor for the support window of the exact version you plan to deploy and who applies security fixes.

A platform your team can operate

Each option asks for a different skill set. Exchange Server runs on Windows Server, OX App Suite v8 runs on Kubernetes with Helm 3.17.0 or newer and Istio or ingress-nginx, and grommunio ships as an openSUSE appliance with ISO or OVA images. Map the platform to the people who will patch, back up and restore it, and confirm whether you have that skill in-house or need a partner for the first build.

Directory integration with LDAP or Active Directory

Your users, groups and distribution lists probably live in Active Directory. grommunio requires the same LDAP or Active Directory as Exchange for its migration script, so mailbox ownership carries over without re-keying users. OX App Suite and other platforms need their own identity integration, which may run through OpenID Connect or SAML. Document which directory is the source of truth and how leavers are deprovisioned.

Client support for Outlook, mobile and CalDAV

Mail replacement fails at the client layer more often than at the server layer. grommunio states that existing Outlook clients keep working through MAPI/HTTP, EWS and Exchange ActiveSync, and that native iOS and Android clients connect through grommunio-sync. Other platforms may need IMAP with CalDAV, which changes how shared calendars and delegates behave. Test each client type, including shared mailboxes and room booking, with a pilot group before setting a cutover date.

Mail export for eDiscovery and retention

Legal holds and retention obligations do not end when the platform changes. Exchange exports to PST with New-MailboxExportRequest, and grommunio's migration script uses the same PST route, so you can keep a copy of every mailbox. Microsoft Purview eDiscovery exports require an E3 or E5 license and search export packages expire after 14 days. Agree with legal and compliance how archives will be stored, searched and kept for the retention period, and test a restore before decommissioning Exchange.

Support and licensing terms

Licensing differs sharply between options. Open-Xchange states that certain modules may carry separate fees set in the license agreement, grommunio sells paid packages through certified partners, and Exchange Server SE requires subscription or Software Assurance licensing. Ask each vendor which features, user counts and support levels are included, who signs the contract, and what happens to your data and licenses if you stop paying.

How Exchange Server SE and Exchange Online change the support question

Exchange Server SE changes the support question from a fixed date to an ongoing decision. Microsoft released Exchange Server Subscription Edition to general availability on July 1, 2025. It follows the Modern Lifecycle Policy, so it has no fixed end date for as long as the configuration stays current, and Microsoft has said it plans no further year-based major versions. Exchange Server 2019 is different: under the Fixed Lifecycle Policy its extended support ended in October 2025, and Microsoft's own pointer for customers is Exchange Server SE or Exchange Online. If you are still on 2016 or 2019, the first step is to inventory every server and confirm its build against Microsoft's current guidance on keeping configurations supported, since an out-of-date configuration can lose support even under the newer policy.

Staying on premises therefore means moving to SE and continuing to pay for it. Confirm the current SE licensing terms directly with Microsoft or your Microsoft partner, including what counts as a server license, how client access licenses are handled and whether your existing Software Assurance or subscription agreements carry over. Those terms drive the recurring cost line, and they should be compared with the cost of Windows Server hosts, storage and upgrade work in the same spreadsheet. Exchange Online, by contrast, moves mail operations to a Microsoft-run service. The trade is recurring per-user subscription cost and reliance on Microsoft's operations in exchange for no servers to patch.

Before choosing either path, confirm three things with Microsoft and your own compliance team: where Exchange Online stores and processes your mailbox data, what contractual data location commitments apply to your tenant, and whether your regulator or public sector framework accepts that location. These commitments are not covered in this page's sources and change over time. If the answer is unclear, a self-hosted platform inside your own data center or cloud account gives you direct control over location, which is one reason to put a dated decision on the calendar now.

Which self-hosted alternatives fit an Exchange 2016 or 2019 replacement

This table compares Exchange Server SE, Exchange Online, OX App Suite and grommunio on where mail lives, what each platform needs to run, which clients connect and how each is licensed. Read it as a shortlist filter: the platform needs and licensing rows usually decide the choice before feature details do.

Option	Where mail lives and platform needs	Client support and licensing model
Exchange Server SE	Mail stays on servers you run on premises, on Windows Server. Confirm current supported OS and hardware requirements with Microsoft before planning.	Outlook and mobile clients connect natively. Subscription or Software Assurance licensing applies to servers and client access licenses.
Exchange Online	Mail is hosted by Microsoft in the cloud, so it does not stay in your own infrastructure. Confirm data residency options with Microsoft.	Outlook and mobile clients connect natively. Licensed as part of Microsoft 365 plans; check current plan terms for eDiscovery export rights.
OX App Suite v8	Runs on a Kubernetes cluster from Helm charts (Helm 3.17.0 or newer), with Istio or basic ingress-nginx, Redis 7.4.x, MariaDB (10.6.x, 10.11.x, 11.4.x or 11.8.x) and distributed storage such as NFS or S3-compatible object storage.	Web, IMAP and CalDAV access, with ActiveSync through a connector. Open-source mirrors are AGPL-3.0, but certain modules may carry separate fees set in the license agreement.
OX App Suite LTS track	Standard releases are supported for 12 weeks. LTS releases are supported until the next LTS plus six months, with v8.47 the current LTS per the support commitment.	Plan upgrades on the LTS cycle. Confirm which LTS line and support tier your contract covers before go-live.
grommunio (Gromox)	Appliance images built on openSUSE (ISO or OVA) or manual and container installs. Works with existing LDAP or Active Directory and can scale out across hosts.	Gromox implements MAPI/HTTP, RPC/HTTP, EWS and IMAP so Outlook connects. ActiveSync and CalDAV/CardDAV are included. Community package covers up to 5 users without manufacturer support.
grommunio paid tiers	Same platform, with support and licenses sold only through certified partners. Confirm the tier that matches your user count and support needs.	Paid per-user subscriptions start from 6 users, with custom Enterprise pricing from 1,000 users per the grommunio pricing page. Ask for a written quote.
Zimbra (for reference)	Core server is open source, but downloadable Zimbra 10 packages require a license key, and the free core is delivered as a FOSS build you compile yourself.	Outlook integration, ActiveSync and archiving sit in the paid Professional tier, so confirm these needs against the license before choosing it.

How to move off Exchange 2016 or 2019 in phases

This sequence moves mail, calendars and contacts off Exchange 2016 or 2019 in controlled stages, so each group is verified before the next one cuts over.

Inventory mailboxes, archives and legal holds
The Exchange administrator lists every user mailbox, shared mailbox, archive mailbox, delegate permission and active legal hold, and records which groups depend on each one. Confirm with the legal or records team which holds must stay intact during the move, because they affect how content is exported and where it is kept. Done when the inventory is signed off by IT and the records owner, and every mailbox has a named migration group.
Choose the target and confirm its requirements
Decide between Exchange Server Subscription Edition, Exchange Online, OX App Suite or grommunio. For a self-hosted target, confirm the platform prerequisites in writing with the vendor. OX App Suite v8 runs on Kubernetes with Helm 3.17.0 or newer, Istio or a basic ingress-nginx option, Redis 7.4.x, MariaDB and a distributed file system. grommunio ships as an openSUSE appliance or can be installed manually or in containers. Done when the target, its platform requirements and its support model are documented and approved.
Build a pilot with a test directory
Create a small test directory and a pilot group of users on the target platform, then run the full export and import path against them. For grommunio, the exchange2grommunio script requires the same LDAP or Active Directory as Exchange, an elevated Exchange Management Shell on Windows Server 2012 R2 or newer, and a shared folder writable by Exchange and mountable on the grommunio server. Confirm that Outlook, mobile and calendar clients connect as expected. Done when pilot users can send, receive and see shared calendars without errors.
Export mailboxes to PST and cloud content to eDiscovery
For on-premises mailboxes, the Exchange administrator runs New-MailboxExportRequest to produce PST files on the agreed share. For cloud content in Microsoft 365, use Microsoft Purview eDiscovery to export mailbox items as PST or .msg files and SharePoint or OneDrive content as native documents with selectable version history. Note that search export packages expire 14 days after creation, and that exporting requires a Microsoft 365 E3 or E5 license. Done when every export request reports completion and the packages are copied to controlled storage before expiry.
Import and reconcile item counts
Import each PST into the target. For grommunio, the script pipes gromox-pff2mt into gromox-mt2exm over SSH and logs successes and failures, so failed batches can be rerun without repeating completed ones. Compare item counts per mailbox between source and target, and review the logs for each failure. Done when every mailbox has a reconciliation record showing matched counts or a documented exception that the owner has accepted.
Run coexistence and cut over by group
Move one migration group at a time, keeping mail flow working between the old and new systems through the transition. Update mail routing, mobile profiles and client settings for each group, and confirm that delegates and shared mailboxes behave correctly after cutover. Keep a rollback path for each group until its users have worked normally for an agreed period. Done when every group is live on the target and the service desk has recorded no open cutover defects.
Decommission Exchange with retention checks
Before turning off Exchange 2016 or 2019, confirm that legal holds, retention obligations and archived records are either migrated or kept in an approved archive. Remove mail routing to the old servers, then retire the servers and their licenses according to the records policy. Ask the compliance lead to sign off that retained data is accessible. Done when the retention checklist is signed and the old servers are removed from production.

Which Outlook and mobile connections each option keeps working

grommunio positions itself as a native Exchange drop-in replacement, and its Gromox server implements the protocols that Outlook uses to talk to Exchange. Gromox provides RPC/HTTP (Outlook Anywhere), MAPI/HTTP, Exchange Web Services, IMAP, POP3 and an SMTP local delivery agent. grommunio's FAQ says existing Outlook clients can stay in place through its MAPI/HTTP, EWS and Exchange ActiveSync support. Mobile and calendar clients use separate components.

Outlook connections: MAPI/HTTP, EWS and RPC/HTTP are the paths to test first, since they determine whether Outlook profiles reconnect without a rebuild.
Native mobile sync: grommunio-sync provides Exchange ActiveSync for native iOS and Android mail, calendar and contacts.
Calendars and contacts: grommunio-dav provides CalDAV and CardDAV for clients that use open standards.
Directory dependency: the same LDAP or Active Directory as Exchange must back grommunio for the migration script and user matching to work.
Paid tiers: the Community package has no manufacturer support and is limited to 5 users, so confirm which support level your client mix needs before going live.

Confirm each client path, including shared mailboxes and delegate access, in a pilot group using your real Outlook versions and mobile devices.

Evidence to keep for the migration and retention record

A migration off Exchange Server 2016 or 2019 leaves a trail that auditors, legal teams and regulators will ask to see long after cutover. The six records below connect the source inventory to the final decommissioning sign-off, and each one should be filed while the work is still happening. DeployOpen prepares these records as part of implementation, but independent auditors and certification bodies issue any audit report or certification.

Source inventory and mailbox counts

Record every Exchange database, server, mailbox type and count before the first export, including primary mailboxes, archive mailboxes, shared mailboxes, resource mailboxes and distribution lists. Capture the Active Directory or LDAP source as well, because grommunio's migration script requires the target to use the same directory as Exchange. Compare these counts with the target after each wave. Ask your team to confirm which mailboxes are on legal hold or subject to retention policies, since those need separate handling.

PST exports and import logs

Keep the PST files produced by New-MailboxExportRequest, the shared folder used to store them, and the import logs written during the transfer to the target. The exchange2grommunio script logs successes and failures for each mailbox, so the log is the proof of which mailboxes moved and which need a second attempt. Store the export and import logs together, with checksums or file sizes, so a later reviewer can match each source mailbox to its target.

Resume log and failed mailbox records

Keep the resume log that exchange2grommunio writes when a run is interrupted, along with a record of each mailbox retried and the outcome of the retry. This shows that no mailbox was skipped silently. Note the reason for each failure, such as an unreadable item, a permission error or a network interruption, and the person who approved the rerun. Ask the implementation team to confirm that the resume logic was tested before production waves began.

eDiscovery export records and expiry handling

If Microsoft Purview eDiscovery is used to collect Exchange items before the move, record each search, the export package, its creation date and its download date. Search export packages expire 14 days after creation, so the record should show when each package was downloaded, stored and deleted from the cloud. Exporting also requires a Microsoft 365 E3 or E5 license, which legal teams should confirm for the period in question.

Support commitment record for the chosen release

Document the release chosen for the target platform, the support basis that applies to it, and the update schedule the operations team will follow. For OX App Suite, a standard release is supported for 12 weeks, while an LTS release is supported until the next LTS release plus six months, so the record should state which type was deployed and when the next upgrade is due. Keep the vendor's support commitment text with the record and confirm the current LTS version directly with Open-Xchange before sign-off.

Backup, restore test and decommissioning sign-off

Keep dated results of restore tests from the new mail platform, including sample mailbox restores and checks that attachments on the distributed file system came back intact. Pair these with the decommissioning sign-off for the Exchange servers, which should confirm that backups of the old environment are retained for the period set by the records and legal teams. Ask the legal and records owners to approve retention periods in writing, because the platform cannot decide them.

What buyers ask before hiring help on an Exchange exit

How long does an Exchange migration take and what drives the timeline?

The duration depends mostly on the number of mailboxes, the total size of mail and archives, how complex the directory is, and the mix of clients your users run. No duration figure is supplied for this page, so ask any provider for a timeline built from your own counts rather than a general number. Large archives and many shared mailboxes extend export and import work, and Outlook users on MAPI or EWS need client testing before cutover. Coexistence planning, where mail flows between old and new systems during the move, adds time that should appear as its own line in the written scope.

Can our own team migrate Exchange without outside help?

A capable internal team can do it, provided it has the skills and time to run the work. For a grommunio move, the supplied migration documentation describes an exchange2grommunio script that exports each mailbox to PST with New-MailboxExportRequest and imports it over SSH, and it logs results so failed runs can resume. Your team would need to supply an elevated Exchange Management Shell on Windows Server 2012 R2 or newer, a shared folder writable by Exchange and mountable on the grommunio server, and a shared LDAP or Active Directory. Plan for testing, rollback and user communication, which are often the parts that take the most effort.

What cost components should we expect in an Exchange exit?

Expect five groups: licensing or subscriptions, platform hosts, storage, support, and migration labor. Exchange Server Subscription Edition is licensed through subscription, while a self-hosted OX App Suite needs Kubernetes, Istio or ingress, Redis, MariaDB and a distributed file system such as NFS or object storage. Hosts, storage, support subscriptions and operations recur every year. Migration labor, testing and cutover are usually one-time. Ask each quote to list these lines separately, with the assumptions behind them, so the recurring total is visible before you sign.

Does grommunio's free Community package fit a small team?

It fits only up to five users, and the supplied pricing page describes it as having no manufacturer support. The page lists Basic at 1.99 euros and Plus at 3.99 euros per user per month from six users, with licenses sold only through certified partners. A team of five or fewer that can carry its own support may start there, but any organization that needs an SLA or vendor escalation should price a paid tier from the start. Confirm the current pricing directly with grommunio, because pricing pages change.

How do OX App Suite module fees affect our quote?

Open-Xchange's Operations Guide states that the right to use certain modules or features may be subject to custom packaging, limitations or separate fees set in the license agreement. This means the base platform price alone may not describe what you will pay. Before comparing quotes, ask each vendor to list every module your requirements touch, such as sharing, mobile sync or archiving, and to state in writing whether each is included, limited or charged separately. Ask for the license terms in the same document as the price so the comparison is like for like.

What should a written migration scope include before we sign?

A written scope should name the systems in and out of scope, the mailbox, calendar, contact and archive counts, and the client types to support. It should list deliverables such as the target platform build, directory integration, export and import runs, test cases, cutover steps and rollback, along with documentation and handover. Ask who owns each dependency, including mail relay, antivirus, DNS and certificates, and which open items would change the price. DeployOpen plans, implements and documents self-hosted platforms in your environment and usually works from a fixed scope agreed in writing before work begins, so ask for that document to define acceptance criteria.

Which Exchange features need checking before we pick a target?

Check the features your users depend on most, not only mail delivery. The supplied facts show grommunio supports MAPI/HTTP, EWS, Exchange ActiveSync, CalDAV and CardDAV, and that Gromox implements RPC/HTTP and IMAP, while OX App Suite is designed around Kubernetes, Redis and MariaDB and needs a distributed file system for attachments and files. Confirm shared calendars, delegates, room booking, retention and any legal hold or eDiscovery needs in a test tenant. Where a feature is not clearly supported, record it as an open item rather than assuming it works.

How DeployOpen runs an Exchange exit under a deadline

DeployOpen plans, implements, integrates, hardens, documents and supports self-hosted open-source platforms inside your own infrastructure. For Exchange Server 2016 and 2019 end of support, we start by agreeing what the replacement must do, then build and test it against your real mail flows before any mailbox moves.

How we scope

We confirm which Exchange versions, mailbox counts and Outlook client types are in use before recommending a target.
We record which clients, shared mailboxes, delegates, archives and compliance holds must survive the move.
Engagements are fixed-scope, with deliverables and timelines agreed in writing before any work starts.

How we build

We deploy the chosen platform in your cloud account, data center or air-gapped network, following your security baseline.
We test client connectivity, calendar sharing, mobile sync and mail relay with pilot users before cutover.
We check storage, database and identity integration so directory sync and authentication behave as they do today.

How we hand over

You receive architecture, configuration and runbook documentation covering the platform and its migration steps.
We document the export, import and rollback procedures so your team can repeat or audit each stage.
We prepare evidence of controls and configuration for your own auditors, who issue any attestation or certification.

How we support

Ongoing support, upgrades and backups are available as a retainer after the handover is complete.
Retainers can cover tracking of platform release and support timelines, so your team plans upgrades before deadlines.
Security testing of the mail platform can be added to the retainer where your risk assessment calls for it.

Exchange Server 2016 and 2019 end of support: self-hosted alternatives