Exchange 2016 Antimalwarescanning Antimalware scanning

Occasional Visitor

Has anyone else had to disable Antimalwarescanning by running Disable-Antimalwarescanning.ps1 to get mail flowing again within the last few weeks? It has happened on 3 different exchange servers on different domains/ environments; 


Message's get stuck in que with the error "message deferred by categorizer"


Mail will not flow until you run the disable ps1 script, if reenabled it stops mail flow; 


Is this service needed? They already have a spam filter setup; 

What needs done to reenabled it?

5 Replies

I just had to run the script on a server :(

Yes. Can Microsoft Support assist as to why we did?

We also faced the similar issue with Exchange 2016CU20 today early morning.
Suddenly it's stopped the mail flow.
I was used below command and resolved the issue.
Set-MalwareFilteringServer -BypassFiltering $True -identity <Server Name>
But it's not good idea to disable or bypass the malware filtering.
MSFT should release the fix.

Anyways thank you.
Anand S
I’m curious how this bug started before 2022 and was not identified by Microsoft since seems related to the date of the signature and how it’s converted.
Same problem. 3 different Exchange environments with 2016 and 2019. Seemed like it happened to me at midnight GMT last night. Y2K bug? LOL.