Microsoft Exchange having issues is not what you want to hear to start off the new year. Looks like there is a solution to emails getting stuck in transport queues and customer action is required to implement.
We have addressed the issue causing messages to be stuck in transport queues of on-premises Exchange Server 2016 and Exchange Server 2019. The problem relates to a date check failure with the change of the new year and it not a failure of the AV engine itself. This is not an issue with malware scanning or the malware engine, and it is not a security-related issue. The version checking performed against the signature file is causing the malware engine to crash, resulting in messages being stuck in transport queues.