There is a new bug for Exchange 2016/2019 onsite servers that stops all mail flow due to a data storage issue. There is no patch from Microsoft yet but there is a workaround, which will disable the Exchange malware scanning capabilities. An update will likely take at least a few days to distribute.
If you are affected by this bug, your onsite Exchange server would have stopped processing inbound/outbound emails starting on 1/1/2022. If you are not having mail flow issues with your Exchange server, you do not need to implement these steps. Please note while disabling this does restore mail flow, it may result in additional spam or malware being delivered to a user if other malware/spam scanning systems are not involved.
- Log in to the server with an administrator account with full access to the Exchange environment.
- Open an Exchange Management Shell (PowerShell) session as Administrator (right-click).
- Run the following 2 commands to disable the Exchange malware scanning system.
Set-MalwareFilteringServer -Identity -BypassFiltering $true
- Run the following command to restart the Transport service and monitor the mail queue to ensure it is delivering queued emails (the queue size should shrink).
- When an update is available and you wish to reinstate the Exchange malware scanning system, run the same commands but with the $false parameter.
Set-MalwareFilteringServer -Identity -BypassFiltering $false
- Restart-Service MSExchangeTransport