Email Stuck in Transport Queues

We are aware of and working on an issue causing messages to be stuck in transport queues on 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.

We are actively working on resolving this issue and expect to release details on how to resolve this issue later today. In the meantime, if your organization performs malware scanning of messages outside of your on-premises Exchange servers (for example, by routing mail through Exchange Online, or by using a third-party message hygiene solution), you can bypass or disable malware scanning on your Exchange servers and clear your transport queues. You should use one of these workarounds only if you have an existing malware scanner for email other than the engine in Exchange Server. See the following articles for details on how to disable or bypass malware scanning:

Our engineers were working around the clock on a fix that would eliminate the need for customer action, but we determined that any change that did not involve customer action would require several days to develop and deploy. We are working on another update which is in final test validation. The update requires customer action, but it will provide the quickest time to resolution.

We expect to have this update to you shortly along with the actions required by you. We are sorry for any inconvenience that this issue has caused.

— The Exchange Team