According to a post on Reddit it seems that Exchange 2016 and Exchange 2019 on-premises are queueing email messages starting januari 1, 2022 at midnight (UTC).
Besides mail queueing you will also see EventID 1106 in the application event log stating “The FIP-FS Scan Process failed initialization. Error: 0x80004005. Error Details: Unspecified error”
This might be a bug is how the date is handles inside the scan engine, causing it to fail after midnight UTC on Januari 1, 2022 (or is it December 31, 2021).
As there is no fix from Microsoft yet, the workaround is to disable anti-malware scanning on all your Exchange servers and restart the Transport service:
CD $ExScripts
.\Disable-AntiMalwareScanning.ps1
Restart-Service MSExchangeTransportUpdate 1 on January 1 at 9PM GMT+1. Microsoft is aware of this issue and working on a solution. Check the Exchange team blog: https://techcommunity.microsoft.com/t5/exchange-team-blog/email-stuck-in-transport-queues/ba-p/3049447
Update 2 on January 2 at 10AM GMT+1. Microsoft has released a solution for this issue. A script can be downloaded from https://aka.ms/ResetScanEngineVersion. This will stop the services, delete the %ProgramFiles%\Microsoft\Exchange Server\V15\FIP-FS\Data\Engines\amd64\Microsoft and the %ProgramFiles%\Microsoft\Exchange Server\V15\FIP-FS\Data\Engines\metadata directories and download new scan engines. This can take a couple of minutes, but the script can be run in parallel on all your Exchange servers.
When the script has finished, check the eventlog and you should see EventID 6036 that all is well.
Although not documented, I had to reboot my Exchange servers. I’ve several other reports from people that they had to reboot too. Another thing, when you disabled the anti-malware as a workaround, you have to re-enable the anti-malware manually. You can check this using the Get-TransportAgent “malware agent” command.
It is also possible to manually update your Exchange servers, this is also documented in the Microsoft article https://techcommunity.microsoft.com/t5/exchange-team-blog/email-stuck-in-transport-queues/ba-p/3049447
One warning though….. All Exchange 2016 and 2019 servers worldwide are suffering from this issue and they all will queue messages. Queues expire after 48 hours, so when not fixed the Exchange servers will generate NDR messages on Sunday night. Worst case scenario, millions of NDRs will be generated which in turn will result in tons of helpdesk calls. If you read this, most likely you have fixed your Exchange servers and it is the Exchange environment of the intended recipients.
Let’s hope it will be quiet again for some time now š
Jaap Wesselius 
You would think Microsoft would have proactively searched for any date-related bugs in all products/platforms in the last 22 years since Y2K š
But now we have a chance to prove the value of the IT department, staff, contractors, and service providers all over again. And ask for more help, staff, budget, 3rd-party support, etc.
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Is it necessary to run the following command after installing the update?
CD $ExScripts
.\Enable-AntiMalwareScanning.ps1
Restart-Service MSExchangeTransport
Thank you in advance for you help.
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Excellent question. If you have previously disabled then yes, it must be enabled again.
You can check using Get-TransportAgent “Malware Agent”
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Getting FIPFS event 2203 after applying the patch.
A FIP-FS Scan process returned error 0x84004003 PID: 14972 Msg: Scanning Process caught exception:
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in our environment we use an external product for malware scanning, so the malware agent (TransportAgtent) is disabled.
The strange thing I see is that besides the FIPFS errors, also the FMS service is ‘unexpectedly terminated.
Although the MSExchangeTransport is registered as ‘DependentService’ that one is still running so, not problems with the queues.
This makes the script (Reset-ScanEngineversion) not completely working because it is not able to start the MSExchangeTransport service (it was not stopped the the ‘Stop FMS’ command earlier.
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