​Microsoft has released hotfix updates to address multiple known issues impacting Exchange servers after installing the March 2024 security updates.

Although the April 2024 HU is optional, it also adds support for ECC certificates and Hybrid Modern Authentication (HMA) for OWA/ECP.

If you have installed the March 2024 SU and have not experienced any known issues fixed in the optional update and do not need the new features, you can wait for the next Exchange Server SU, which will also include these hotfixes.

“The April 2024 HU includes the same security updates as the March 2024 SU, while addressing known issues with the March 2024 SU,” the Exchange Team explained.

“If you did not install the March 2024 SU, you can install the April 2024 HU directly and skip the March 2024 SU.”

With this month’s hotfixes, Redmond fixed a known issue causing download domains to no longer work as expected in some Microsoft Outlook. This caused inline images to no longer be displayed on Outlook on the Web (OWA) and attachments not being downloaded using the OWA client.

The company also addressed a bug that triggered “We can’t open this document” errors and blocked Microsoft Word document previews in Outlook on the Web (OWA).

The list of issues caused by the March 2024 security updates and addressed in April’s Exchange hotfixes also includes:

Microsoft is still working on a fix for another issue where calendar printing in OWA might not work unless the CTRL+P keyboard shortcut is used.

The April 2024 hotfixes are available for Exchange Server 2019 CU13 and CU14 and Exchange Server 2016 CU23.

In January, Redmond announced the end of mainstream support for Exchange Server 2019, saying it will keep releasing patches to fix the latest discovered security issues but will no longer accept requests for bug fixes and Design Change Requests (DCR).

Exchange Server 2016 reached its mainstream end date in October 2020 but is under extended support until October 2025, just like Exchange Server 2019.

The company now provides Microsoft 365 migration information on its documentation site and guidance to help global admins decide the migration path in Exchange Online.