Unable to change mailbox permissions

Question

Hello!

We inherited a Hybrid Exchange environment. It consists of a local Exchange Server (version 15.0 (internal version 1473.3)) and M365. All email addresses have been migrated to M365 and ADSync exists

Copy to M365.

The problem we encountered is that even as global administrators and Exchange administrators in M365, we are unable to edit the permissions of any user email. Performing this operation through M365 management center will only return

A message indicating that there is a problem. If we try in PowerShell, we will receive a message saying 'User is not allowed to call'.

We are trying to understand if this is an issue with M365, or are we trying to make permission changes from the wrong location?

In a hybrid environment where all mailboxes have been migrated, where should you change mailbox permissions?

Did we do anything else wrong here?

Answer 1

If you are syncing from onprem to Azure you have to make the changes on-prem

https://learn.microsoft.com/en-us/exchange/decommission-on-premises-exchange

See all the options listed including if you dont need to sync any longer

But.. When you say you are updating permissions, which permissions?

Because if you giving full access or send as perms to a 365 mailbox, that is done in 365 directly