Happy new year 2022! And I wanted to share that if you have the latest patch installed in your Exchange you might have run into a YK22 bug !
The Microsoft Filtering Service got hit by a bug in it’s patch system.
To resolve in the short term please run;
Set-MalwareFilteringServer -BypassFiltering $True -identity <server name>
Disable-AntimalwareScanning.ps1 -forcerestart from the script folder.
The bug is explained there; https://old.reddit.com/r/sysadmin/comments/rt91z6/exchange_2019_antimalware_bad_update/ but it’s a variable error from the year 2021 to 2022 that make a long overflow vs an unsigned long that would had been ok.
Thanks everyone for reading, and good year !! 🙂
Update; it’s now fixed;