Tag Archives: Exchange2019

Exchange 2016 & 2019 ESU

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In a somewhat surprising move yesterday, Microsoft announced there will be an Extended Security Update program for Exchange Server 2016 and Exchange Server 2019. The ESU is to cater to organizations that indicate they need some more time to move away from Exchange 2016/2019. I will not comment on the fact that these organizations had a few years to get current on Exchange 2019, which would lead them to having a smooth upgrade path now to Exchange SE, or even move to Exchange Online.

Extended Security Update

You might already be familiar with ESU programs, which are common for Windows clients and Windows Server, a.o. That said, Exchange also had its share of post-lifecycle (out-of-band) updates, such as the Hafnium security updates for Exchange 2013 and even Exchange 2010. These updates were developed and made available without any obligation as some of the updates applied to products that were past their end-of-support date.

Now, the ESU program for Exchange 2016/2019 is an official extension to keep receiving published security updates for Exchange 2016/2019. To receive these, organizations can purchase a 6-month ESU for their Exchange servers. For this, they need to contact their Microsoft account manager starting August 1st, 2025. Do note that there is no guarantee that, within this period, security updates will get published, as this is entirely driven by circumstances and urgency, of course.

To make it clear: The ESU program is not an extension of support. You cannot contact support for any incident with Exchange 2016/2019 in the ESU period. That is, unless it relates to an SU that gets published during the ESU period. Thus, ESU is more for peace of mind when it comes to security, when you can live without expecting support.

The ESU period ends April 14th, 2026, 6 months after Exchange 2016 and Exchange 2019 go out of support. It is possible to get ESU after August 1st and during the 6-month ESU window. This flexibility may lead to organizations taking a gamble, waiting for SU to appear, only to get ESU when the first SU arrives. Given that corporate purchasing processes might take some time and CUs usually come with some urgency to implement, this is not something I would recommend.

I would also not recommend seeing this ESU window as an opportunity to take it easy. The support date stands, which is what most organizations find most important. So, keep migrating, whether to Exchange SE directly or via Exchange 2019 CU15, or to Exchange Online.

Skype for Business

Skype for Business is iņ the same boat regarding lifecycle, and also has a similar ESU program. For more information, click here.

Hotfix Updates Exchange 2016-2019 (May2025)

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The Exchange product group released the May 2025 Hotfix Updates for Exchange Server 2019 and Exchange Server 2016.

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 app support added in the April hotfixes.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU15Download15.2.1748.26KB5057651KB5050672
Exchange 2019 CU14Download15.2.1544.27KB5057652KB5050673
Exchange 2016 CU23Download15.1.2507.57KB5057653KB5050674

Changes

Issues addressed in these hotfixes are:

Dedicated Exchange Hybrid Application

A gentle reminder that since the April 2025 security updates, Exchange hybrid supports the dedicated Exchange hybrid app. The dedicated Exchange hybrid app becomes mandatory in October 2025 for continued cross-premises functionality (free/busy, a.o.). To make the required changes related to the Graph permissions model you have some more time, as that will become required in October 2026. For more information, please visit this link.

Hotfix Updates Exchange 2016-2019 (Apr2025)

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The Exchange product group released the April 2025 Hotfix Updates for Exchange Server 2019 and Exchange Server 2016. Hotfix updates do not contain security fixes. Instead, this hotfix introduces support for the updated Exchange Hybrid Application model.

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU15Download15.2.1748.24KB5050672
Exchange 2019 CU14Download15.2.1544.25KB5050673
Exchange 2016 CU23Download15.1.2507.55KB5050674

Dedicated Exchange Hybrid Application

Instead of relying on the default Office 365 Exchange Online application in Entra ID, the new model leverages a dedicated application in Entra ID to support Exchange Hybrid. By creating a new dedicated, unique application ID per tenant, instead of relying on the well-known application identifier 00000002-0000-0ff1-ce00-000000000000, allows organizations to decide when to move from EWS to Graph permissions.

To implement the dedicated Exchange Hybrid Application and configure all related aspects, the product group published a script, ConfigureExchangeHybridApplication.ps1 (part of the hotfix or available here). This script can take care of parts or all of the configuration. An extensive article explaining the steps and script usage is published here, so there is no need to repeat that information.

In addition, as part of the move to Graph from Exchange Web Services, the new Exchange Hybrid application will eventually leverage Graph instead of Exchange Web Services. Since Exchange still lacks functionality in the Graph area, the new app still requires blanket EWS permission full_access_as_app. But consider this a first step in the transition process, and expect permissions to change to Graph API permissions in the future.

Moving away from the common application, which has been around for a while, may impact existing scripts and procedures with hard references to its identifier. You need to anticipate this change by making the reference independent and dynamic. To determine this identifier, check for an Entra application named ExchangeServerApp-<Organization Guid>, provided you used the ConfigureExchangeHybridApplication script to create it.

Co-Existence

Organizations running Exchange Hybrid requiring rich co-existence must implement this April 2025 HU before October 2025 for continued functionality. This includes upcoming changes in Graph permissions (ETA October 2026). This may create an additional task when running Exchange Hybrid as part of a long-term hybrid deployment or when migrating to Exchange Online. Failure to do so may result in unpleasant surprises, such as broken Free/Busy sharing functionality.

Exchange SE

The change in the Exchange Hybrid Application model will propagate to Exchange SE. Exchange SE is the successor to Exchange 2019 and is expected to become available later this year, replacing the soon-to-be-out-of-support Exchange Server 2019 and Exchange Server 2016 versions.

Exchange 2019 CU15 (2025 H1)

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The Exchange Team released Exchange Server 2019 Cumulative Update H1 2025, or CU15, almost one year after CU14. CU15 will also be the last CU for Exchange 2019, which will become end-of-life in October this year. Customers staying on-premises are recommended to use the remaining time this year to upgrade to this CU level to have a smooth transition to Exchange Server Subscription Edition (SE) later this year. The official announcement can be found here.

Features
Apart from fixes and updates, including those from the security update of November (e.g. AMSI changes), this Cumulative Update for Exchange 2019 introduces some feature changes:

  • Exchange 2019 CU15 and CU14 are now supported on Windows Server 2025. This includes environments running domain controllers running Windows Server 2025. This allows organizations to consider using Windows Server 2025, not having to look at migrations because of the underlying operating system when Exchange SE. Note that Windows Server 2025 is not currently a supported Forest Functional Level.
  • As announced in the roadmap article, the CU15 setup contains an Exchange 2013 coexistence block, preventing it from being deployed in organizations running Exchange 2013. The consequence is that when you are still on Exchange 2013, you might need to migrate to CU14 first (it can be on WS2025). After that, you can upgrade those CU14 servers to CU15 after decommissioning Exchange 2013 servers.
  • Certificate Management has returned to the Exchange Admin Center.
  • Partial TLS 1.3 support on Windows Server 2022 and later. TLS 1.3 is supported for all protocols except SMTP; SMTP support is expected in a future update. Deploying CU15 on Windows Server 2022 or later will enable TLS 1.3 by default; disable it when needed per these instructions.
  • DocParser replaces Oracle Outside In Technology (OIT). This library extracts text from emails during transport for purposes of Data Loss Prevention and Exchange Transport Rules.
  • Feature Flighting is a server-side component allowing selected changes to be deployed and managed through deployment rings. This resembles how updates can be managed for other products, such as Microsoft Office or Windows. Note that CU15 just introduced the Feature Flighting engine with a PING feature for testing purposes. No features are being flighted until after Exchange SE, which aligns with the promise of Exchange 2019 CU15 running the same code as Exchange SE. Feature Flighting is optional and can be disabled when needed. When diagnostics data collection is enabled, additional data related to Feature Flighting will be included.
  • Exchange SE will support Exchange 2019 product keys. Previously, it was announced that CU15 would accept SE product keys. This dependency order was changed to ease the migration path. New keys are now only required per Exchange SE CU1.


Download
Below is the link to the update. The columns Schema and AD indicate whether the CU contains changes to Schema (/PrepareSchema) and Active Directory (PrepareAD) compared to the previous CU. Refer to the Exchange Schema page for schema and related versioning information.

VersionBuildKBDownloadSchemaAD
Exchange 2019 CU1515.2.1748.10KB5042461DownloadNY

Fixes

  • 5047359 Clean up old Exchange OWA files automatically to free up disk space
  • 5047361 Inline images and text attachments are not visible in OWA
  • 5047402 Online Archiving bypasses the InternetWebProxy setting in Exchange 2019
  • 5047995 MFNs are not sent to remote domains
  • 5047997 Wrong server version displayed in POP and IMAP logoff strings
  • 5048017 RecoverServer operation fails in Exchange Server 2019
  • 5048019 “NullReferenceException” error and Managed Store stops responding
  • 5048020 Calendar print doesn’t work in OWA from Exchange 2019 CU14 onwards
  • 5048021 HTML message is corrupted if <&quote;> is included
  • 5048072 “Enabled Extended Protection” message when you run setup with prepare*​​​​​​​ command
  • 5047994 German umlauts in the Subject are replaced by a question mark
  • 5047358 Group Metrics generation doesn’t finish in multidomain environment

Notes

  • If Cumulative Updates contain schema changes compared to the Cumulative Update you currently have deployed, you need to run Setup with /PrepareSchema. If they contain Active Directory changes, you need to run /PrepareAD. Alternatively, permissions permitting, you can let Setup perform this step. Consult the Exchange schema versions page for schema and related versioning information.
  • When upgrading from an n-2 or earlier version of Exchange or an early version of the .NET Framework, consult Upgrade Paths for CU’s & .NET.
  • Remember to put the Exchange server in maintenance mode prior to updating. Regardless, setup will put the server in server-wide offline mode post-analysis before making actual changes.
  • When using Exchange hybrid deployments or Exchange Online Archiving (EOA), support requires you to trail at most one version (n-1).
  • Ensure the Windows PowerShell Script Execution Policy is set to Unrestricted during deployment. This to prevent installation failures due to the inability to validate script signatures.
  • To speed up the system update process without internet access, you can follow the procedure described here to disable the publisher’s certificate revocation checking.
  • Cumulative Updates can be installed directly; no need to install RTM before installing Cumulative Updates.
  • Once upgraded, you can’t uninstall a Cumulative Update or any of the installed Exchange server roles.
  • The recommended upgrade order is internet-facing, non-internet-facing servers first, followed by Edge Transports.

Caution
As for any updates, I recommend thoroughly testing updates in a test environment before implementing them in production. When you lack such facilities, hold out a few days and monitor the comments on the original publication or forums for any issues.

Security Updates Exchange 2016-2019 (Nov2024)

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NOTICE (Nov27): The SUs have been re-released. The v2 adds additional control over the X-MS-Exchange-P2FromRegexMatch header, which is set for messages with a non-RFC5322 compliant P2 FROM header. Install these on your Exchange server, also if you already deployed the v1 SU to benefit from the additional control.

The Exchange product group released November 2024 updates for Exchange Server 2016 and 2019.

The vulnerabilities addressed in these Security Updates for Exchange Server are:

VulnerabilityCategorySeverityRating
CVE-2024-49040SpoofingImportantCVSS:3.1 7.5 / 6.7

The v2 Security Updates for each supported Exchange Server build are linked below:

ExchangeDownloadBuildKBSupersedes
Exchange 2019 CU14 Download15.2.1544.14KB5044062
KB5049233		KB5036401
Exchange 2019 CU13Download15.2.1258.39KB5044062
KB5049233		KB5036402
Exchange 2016 CU23Download15.1.2507.44KB5044062
KB5049233		KB5036386

Added Features

Anti-Malware Scan Interface (AMSI) integration

The ability of products that use the Exchange Server AMSI integration to perform additional tasks on message bodies. The feature is disabled by default. You can enable it on a protocol base like Exchange Web Services or PowerShell. More information on this feature here.

Non-RFC5322 compliant header detection

Similar to the change in Exchange Online mentioned in MC886603, after installing this SU, messages with a non-compliant P2 FROM header (RFC5322) will be detected. Unlike Exchange Online, which will drop these messages, Exchange will add a header that can be used in transport rules as organizations see fit. To be compliant, organizations should ensure messages with multiple From addresses include a Sender header. More information here.

Elliptic Curve Cryptography (ECC) certificate support

ECC certificates can now be used on Edge Transport servers and bound to the POP and IMAP services. Note that unlike the previous implementation, which required enabling using New-SettingOverride, they are now configured through a registry key, i.e.

New-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\ExchangeServer\v15\Diagnostics" -Name "EnableEccCertificateSupport" -Value 1 -Type String

More information here.

Microsoft Information Protection Client (MSIPC)

MSIPC will now ne enabled by default, replacing Microsoft Digital Rights Management (MSDRM) for information rights management.

Fixed Issues

Apart from security fixes and added features, these Security Updates also correct the following issues:

Issue FixedExchange 2016Exchange 2019
Journal report decryption doesn’t decrypt attachment in journal mailboxYesYes
Error after adding support for AES256-CBC–encrypted content in August 2023 SUYesYes
Exchange can’t decrypt IRM messagesYes
Server with PowerShell_ISE doesn’t serialize when connecting to EMSYesYes
Email sent through Pickup folder displays admin versionYesYes
CSR created by Exchange are signed with outdated Encryption algorithmYesYes
OWA displays incorrect time zone for AmmanYesYes
Kazakhstan changes to single time zone in 2024YesYes
Moderated messages are marked as expired after they are approved or rejectedYes
Exchange Transport Rules and Data Loss Prevention rules don’t work after installing November 2024 SU V1YesYes

Notes

  • Security updates are Cumulative Update level specific. You cannot apply the update for Exchange 2019 CU14 to Exchange 2019 CU13. When downloading, the security update will carry the same name for different Cumulative Updates, and I suggest tagging the file name with the CU level when archiving it, e.g., Exchange2019-CU14-KBXXXXXX-x64-en.msp.
  • Like Cumulative Updates, Security Updates are cumulative, and you only need to install the latest SU for your CU.
  • If you have deployed Exchange Management Tools to manage your on-premises Exchange Servers or installed the tools after removing the Last Exchange Server for recipient management, it is recommended that you apply the Security Update. Be aware of a few cmdlet piping issues mentioned here.

On a final note, as with any patch or update, it is recommended that you apply it in a test environment before implementing it in production. However, it is not recommended to wait for regular maintenance cycles when it concerns security updates and follow a more agile approach; the ratings indicate the level of urgency.