Exchange Server 2016 and 2019 reach end of support on October 14, 2025, and in hybrid environments that date is starting to feel very real. I keep running into tenants where nearly every mailbox already lives in Exchange Online, yet the last on-premises Exchange server is still running. Sometimes that comes down to caution. Sometimes there's one leftover workload nobody wants to touch. Retiring Exchange on-prem has a clearer path than it used to, but as usual, the practical details decide whether it works.

End of support also affects hybrid tenants that only manage recipients

If you still run Exchange Server 2016 or 2019 to manage on-premises recipient objects (users, groups, contacts), you need a concrete timeline for the coming year. After end of support, the server gets no more security updates and no support. That raises the compliance and security stakes, particularly in hybrid setups where Exchange is still the management endpoint for AD-based recipients. People often miss one point here. Even when every mailbox has moved to Exchange Online, you should keep managing recipient objects with an Exchange-aware tool. Otherwise attributes drift out of sync and you end up with issues like missing proxy addresses.

For this recipient management scenario, Microsoft provides the Exchange Management Tools package (available since Exchange 2019 CU12), so you don't need a full Exchange server just to maintain those AD attributes. The official documentation covers details and requirements. Keep in mind that the package handles recipient management only. SMTP relay, transport rules and public folders are not part of it, and if you need any of those, you still need a real Exchange server on-prem.

The last Exchange server can go once nothing depends on it

Two conditions have to be met. First, all mailboxes, including shared, resource and archive mailboxes, must be fully migrated. Second, no app, scanner or SMTP source may still relay through an on-prem Exchange box. In my projects there's almost always one last special case hiding somewhere. The on-prem Exchange server stays until every mailbox and recipient object is cloud-only and all SMTP relay has moved (to Exchange Online, a device, or a third-party solution). If you still need to manage Exchange attributes for AD users, the Management Tools package is the best option. Once nothing depends on on-prem Exchange anymore, you can shut it down completely.

The diagram below shows the classic decision tree for decommissioning the last Exchange server in a hybrid setup:

flowchart TD
    AllMailboxes["All mailboxes migrated?"] -->|"No"| ExchangeStays["Exchange server must stay"]
    AllMailboxes -->|"Yes"| SMTPRelay["Is SMTP relay needed on-prem?"]
    SMTPRelay -->|"Yes"| ExchangeStays
    SMTPRelay -->|"No"| RecipientMgmt["On-prem recipient management needed?"]
    RecipientMgmt -->|"Yes"| MgmtTools["Use Management Tools package"]
    RecipientMgmt -->|"No"| Decom["Decommission Exchange server"]

Figure: Decision tree for retiring the last Exchange server in a hybrid tenant.

The Management Tools package handles recipient management without a full server

The Exchange Management Tools package fits when you have no on-prem mailboxes left but still need to manage Exchange attributes for AD-synced objects. It's a lightweight install and needs no license as long as no server roles (mailbox, transport, etc.) are active. It requires Exchange Server 2019 CU12 or newer on a supported Windows Server. I'd go with CU15, because only from there will an in-place upgrade to the upcoming Exchange Server Subscription Edition be available. If you're still on Exchange 2016, you have to migrate to 2019 before you can use the package or its successor at all.

Tip from the field: Make absolutely sure you haven't missed any leftover mailboxes, forwards or application accounts. Run exports from the Exchange Admin Center or PowerShell and check them twice. Shared mailboxes are especially easy to overlook, and they tend to cause strange problems later on.

Keep an eye on your server's build numbers and release dates so you can plan around that final year of updates.

Some organizations still need a local Exchange server

Some organizations can't or won't retire Exchange on-prem completely. If you still have on-prem mailboxes for line-of-business apps, scan-to-email or regulatory reasons, the server stays. The same applies to on-prem SMTP relay scenarios that can't move to Exchange Online for technical or licensing reasons. In those cases you have to be ready to upgrade to the next generation. Microsoft has announced the Exchange Server Subscription Edition as the successor, with an in-place upgrade from 2019 CU14/15 once it ships. As of early January 2025, though, it isn't available yet.

For hybrid setups that still need on-prem mailboxes, the checklist looks like this:

  • Bring Exchange Server 2019 up to CU15
  • Plan for the next version and watch for its release
  • Review and document all SMTP relay and application integrations
  • Deal with the security and compliance risks that come with end of support

2025 is the right year to finish the Exchange clean-up

In my view, 2025 should be the year you finally deal with the last Exchange dependencies. If mailboxes, legacy apps or SMTP relays are still on-prem, now is the time to check whether they can move to Exchange Online, Azure or another platform. A thorough assessment almost always makes it clear whether you need to keep Exchange on-prem. Once you know the steps, a clean and safe decommissioning is entirely doable, and I'm seeing more tenants manage it than ever before. This is a good moment to leave the old Exchange baggage, and the old habits that came with it, behind.