Summary
When Microsoft Exchange Server is deployed in a hybrid configuration, features such as free/busy sharing, MailTips, and Profile pictures are made available between Exchange Server and Exchange Online. This configuration ensures a seamless user experience. These features are automatically configured the first time that the Hybrid Configuration Wizard (HCW) runs.
To enable hybrid functionality, Exchange Server uses a shared service principal together with Exchange Online for secure communication. However, this process will be revised in the near future as Exchange Server transitions from using the EWS API to using the Microsoft Graph API to request data from Exchange Online. To prepare for this significant change, a configuration update is required in your Exchange hybrid environment.
Resolution
To apply this change, install the following hotfix updates:
- Hotfix update for Exchange Server 2019 CU15: April 18, 2025 (KB5050672)
- Hotfix update for Exchange Server 2019 CU14: April 18, 2025 (KB5050673)
- Hotfix update for Exchange Server 2016 CU23: April 18, 2025 (KB5050674)
For more information about how to configure the Exchange Hybrid Application, see Configure Exchange Hybrid Application.