Exchange Server 2019 CU15 Apr25HU
Hotfix update for Exchange Server 2019 CU15: April 18, 2025 (KB5050672)
Hotfix update for Microsoft Exchange Server 2019 CU15 was released on April 18, 2025. This update introduces non-security fixes and new features.
In this article, we will cover the contents of the Microsoft Exchange Server 2019 CU15 Hotfix update.
Featured Features
Exchange Hybrid Dedicated App in Entra ID for Exchange 2016 CU23 and Exchange 2019 (CU14 and CU15)
When Microsoft Exchange Server is configured in hybrid mode, users can seamlessly share information such as calendar status (free/busy), MailTips alerts, and profile photos between Exchange Server and Exchange Online. This integration allows both environments to function as a single system. This functionality is automatically implemented when the Hybrid Configuration Wizard (HCW) is first run.
This hybrid communication infrastructure is implemented using a common service principal to securely exchange data between Exchange Server and Exchange Online. However, Microsoft is planning a significant change to this structure. Exchange Server will now use the Microsoft Graph API instead of the legacy EWS API to retrieve information from Exchange Online.
Fixed Issues
This update fixes the issue that occurred in the November 2024 Security update.
InvalidTimeZoneException after installing November 2024 SU (Version 1 or Version 2)
After installing the November 2024 Security Update (SU) for Microsoft Exchange Server (Version 1 or Version 2), you may encounter some issues handling calendar-related files (files with .ical or .ics extensions). These issues may include the following:
- Inability to preview these files or add them to the calendar
In these cases:
- Transport service restarts,
- Relevant emails are sent to the poison queue,
- An error message is displayed in the event log as follows: Microsoft.Exchange.ExchangeSystem.InvalidTimeZoneException: Time zone id already exists
Known Issues
Edge Transport service stops responding after installing November 2024 SU
After installing the Microsoft Exchange Server November 2024 Security Update (Version 1 or version 2), the Edge Transport service (EdgeTransport.exe) intermittently becomes unresponsive and automatically restarts after a short while.
This typically occurs when Exchange attempts to decrypt emails from external sources that have been encrypted with Azure Rights Management (Azure RMS). This problem is particularly prevalent on systems with Journaling configured and when the Journal Report Decryption feature is enabled.
In cases where the problem occurs:
Relevant encrypted messages are moved to the poison-message queue for security reasons.
The following type of record is generated in the Exchange server event log:
- Log Name: Application
- Source: MSExchangeTransport
- Event ID: 10003
- Task Category: PoisonMessage
- Level: Error
- Description: The transport process failed during message processing with the following call stack: Microsoft.Exchange.Data.Common.LocalizedException: Agent '' encountered an unexpected error while
handling event ''. ---> Microsoft.Exchange.Data.RightsManagement.RmException: Failed to fetch the key handle and properties.
Temporary Solution
Starting with the November 2024 Security Update, MSIPC is enabled by default. To work around this issue, you can disable the Microsoft Information Protection Client (MSIPC).
New-SettingOverride –Name "DisableMSIPC" -Component Encryption –Section UseMSIPC –Parameters @("Enabled=false") -Reason "Disabling MSIPC stack"
Get-ExchangeDiagnosticInfo -Process Microsoft.Exchange.Directory.TopologyService -Component VariantConfiguration -Argument Refresh
Restart-Service MSExchangeTransport