https://www.bleepingcomputer.com/news/security/microsoft-urges-admins-to-patch-on-premises-exchange-servers/

Microsoft urged customers today to keep their on-premises Exchange servers patched by applying the latest supported Cumulative Update (CU) to have them always ready to deploy an emergency security update.

Redmond says that the Exchange server update process is "straightforward" (something that many admins might disagree with) and recommends always running the Exchange Server Health Checker script after installing updates.