Error after adding support for AES256-CBC–encrypted content in August 2023 SU

Symptoms 

After you enable support for AES256-CBC–encrypted content by installing the Microsoft Exchange Server August 2023 Security Update (SU), Exchange Server logs the following error event in the event log when an email message is processed by the transport pipeline, regardless of whether the message is encrypted:

Resolution 

To fix this issue, install the following security update:

• Description of the security update for Microsoft Exchange Server 2019 and 2016: November 12, 2024 (KB5044062)