https://www.bleepingcomputer.com/news/microsoft/microsoft-exchange-year-2022-bug-in-fip-fs-breaks-email-delivery/

Microsoft Exchange on-premise servers cannot deliver email starting on January 1st, 2022, due to a "Year 2022" bug in the FIP-FS anti-malware scanning engine.

Starting with Exchange Server 2013, Microsoft enabled the FIP-FS anti-spam and anti-malware scanning engine by default to protect users from malicious email.