Released: April 2021 Exchange Server Security Updates

luke_q7 Thing is - there is no such thing as "Exchange express". If your organization is in fact in Hybrid, then you have an Exchange Server on-premises. I take it you use it for management, right? Which means that EAC, or Exchange PowerShell have to connect somewhere on-premises. So Exchange services and IIS virtual directories are running somewhere. Now, you could also have a "Management tools only" machine which only has Exchange Management Tools installed, but in that case, those management tools still need somewhere on-premises to connect to.

I am making an assumption here that you run Exchange Admin Center and/or PowerShell on-premises? If yes - there is Exchange Server somewhere. That is the machine that needs updating if you are in hybrid.