The Exchange product group released the May 2026 Hotfix update for Exchange Server SE. Hotfix updates do not contain security fixes, but address issues. They also might introduce or add support for functionality changes, such as dedicated Exchange hybrid application support.
Changes
The change introduced in this hotfix is:
Dedicated Exchange Hybrid Application
The dedicated Exchange hybrid application supports Exchange Web Services workflows, enabling rich coexistence functionality. This hotfix adds Graph-based workflow support for rich co-existence features between Exchange SE and Exchange Online. After installing the May 2026 update on all your Exchange SE servers, make sure you configure and enable the dedicated Exchange Hybrid application in Entra.
The support page lists WW as the tenant environment that currently supports Graph-based workflows, e.g. not GCC nor DoD. In addition, rich coexistence still partially uses EWS as shown in the following table taken from the dedicated hybrid application page.
| Functionality | EWS supported | Graph supported |
|---|---|---|
| Free/Busy | Yes | Yes |
| MailTips | Yes | Partial (Automatic Replies only) |
| Profile Pictures | Yes | Yes |
| Move to Archive (Archive Mailbox in cloud) | Yes | No |
Important: If you previously configured the dedicated Exchange Hybrid application, you need to rerun the ConfigureExchangeHybridApplication.ps1 script. This will enable the new Graph-based workflow. Detailed steps for accomplishing this are described here.
What about Exchange 2019 and Exchange 2016?
Exchange 2016 and 2019 are out of support and will not receive this update when you are part of the ESU program. Therefore, with the upcoming deprecation of Exchange Web Services in Exchange Online, you must keep allowing EWS in your tenant as of October 2026 – when EWS gets disabled – and make sure you plan to have migrated to Exchange SE by April 2027 for continued rich coexistence functionality, when EWS gets permanently disabled in Exchange Online.