Exchange Server: Now it’s serious, Exchange Web Services is switched off
An upcoming update for Exchange Server changes the fundamental communication technology in hybrid company networks. Microsoft is rigorously shutting down a two-decade-old interface. This has fatal consequences for many older systems.
Functional update instead of security patches
An important update has been available for on-premises email system administrators since early May 2026. The May 2026 hotfix update does not contain security updates for Exchange Server, but provides important new features and bug fixes. The package is aimed at operators of hybrid environments in which local servers are linked to cloud services. Essentially, it’s about changing communication technology. Previously, the systems used the so-called EWS interfaces (Exchange Web Services) for extended coexistence functions between local servers and the cloud. This older technique is now gradually being replaced by REST-based calls via the more modern Graph API. This means that functions such as availability and profile information should work more reliably in the long term.
As Microsoft reports, the update is a necessary step for the future. Switching to the new interface is mandatory because the old web services in Exchange Online will be completely deactivated in April 2027. Web Services were introduced in 2007 to provide developers with a standardized way to interact with mailboxes. For almost two decades, they have formed the backbone of numerous third-party applications. Technological developments and increased security requirements now make the transition to the Graph API unavoidable, as it offers more modern authentication methods and better performance with large amounts of data. This means a turning point for users of the older versions Exchange 2016 and Exchange 2019. Regular support for these systems has already expired. You will no longer receive the new feature update. If these servers are not updated to the current subscription edition in time, the hybrid connections will finally be terminated in spring 2027.
Preparations for administrators
Before installing the hotfix update, we recommend taking a detailed inventory. The Health Checker script can be used to check whether the servers are up to date. After the update has been applied, the permissions of the dedicated hybrid application must be switched to the granular permission model of the Graph API. Depending on your system configuration, it may be necessary to run specific commands in the PowerShell console. One advantage of the new structure is the more precise allocation of rights, which consistently implements the principle of least privilege. At the same time, the transition process requires careful planning by IT departments, as misconfigurations can disrupt email traffic.
