Exchange Server 2016 and 2019 end of support: options

Exchange Server 2016 and 2019 reached end of support on October 14, 2025. Since then, Microsoft no longer releases security updates for these versions. The servers keep sending and receiving e-mail, but every vulnerability discovered since remains open.

For a small business that still hosts its e-mail on premises, the question is no longer whether to act, but how. Two paths are supported: Exchange Online in Microsoft 365, or Exchange Server Subscription Edition on premises.

End of support: what are the risks of staying on Exchange 2016 or 2019?

• A server that is exposed to the Internet by nature: incoming e-mail, Outlook on the web and mobile sync all go through it.
• Vulnerabilities that will no longer be fixed, even though on-premises Exchange has already been the target of large-scale exploitation campaigns, notably in 2021.
• Cyber insurance questionnaires that ask whether end-of-support systems are still in use.
• The nFADP, which requires security appropriate to the risk: an unmaintained server holding all of the company's correspondence is hard to reconcile with that.
• Software vendors and backup tools that may stop supporting these versions.

Exchange Online: moving e-mail to Microsoft 365

For most small businesses, this is the simplest path: e-mail is hosted and maintained by Microsoft, updates are applied without intervention, and there is no server left to replace. Mailboxes are migrated, then the domain's DNS records are switched over.

Microsoft operates data centers in Switzerland; check in the admin center where your tenant's data is stored. Also plan for devices and software that send e-mail through the local server (scanners, business software), as well as public folders.

Exchange Server Subscription Edition: staying on premises

Exchange Server Subscription Edition (SE) is the on-premises successor to Exchange 2019. It remains supported as long as you hold subscription licenses, or Software Assurance, for the servers and the users.

From an up-to-date Exchange 2019, moving to SE is an in-place upgrade. From Exchange 2016, you need to install new servers and move the mailboxes to them. This path makes sense mainly when a constraint requires keeping e-mail on your premises; it also keeps the burden of hardware, backups and updates.

Migrating from Exchange 2016 or 2019: the steps

Whatever the target, the migration follows the same main steps. The schedule depends on the number of mailboxes and on the applications connected to the server. If accounts are synchronized from an on-premises Active Directory, removing the last Exchange server requires specific preparation.

What if the migration cannot happen right away?

If a constraint delays the migration, reduce exposure in the meantime: latest updates installed, access to Outlook on the web restricted or placed behind additional protection, closer log monitoring, tested backups. These are temporary measures, with an end date written into the plan.

Finally, think about archiving: e-mails that serve as accounting records or business correspondence must remain accessible for the legal retention period, including after the old server is removed.