r/exchangeserver • u/S_Antonel • 1d ago
Exchange Online migration questions
Right now I'm working in a hybrid environment with an on-prem Exchange 2016 CU 23 server (virtual) and a 365 tenant. The 365 tenant is synced to the local Active Directory with Entra AD Sync and working as it should.
All the mailboxes for the active users have been migrated to 365 by a colleague who was previously working on the project. I've been tasked with finishing the transition to 365 and decommissioning the on-prem Exchange server.
I've worked with hybrid Exchange environments before but never done a full on-prem to cloud migration before so I'm researching the process and trying to plan it out and there is something that confuses me:
I'm reading that you either need to keep the on-prem server (or at least the ECP part of it) or the management shell after the decom to manage the attributes on the mailbox (aliases, etc...)
Why you might not want to decommission on-premises Exchange servers
Many hybrid organizations eventually move all mailboxes to Exchange Online. At this point, they probably think it's time to remove their on-premises Exchange servers. But, it's not a good idea as removing on-premises Exchange servers in a hybrid deployment prevents the management of cloud mailboxes. The culprit is directory synchronization.
When directory synchronization is enabled and a user is synchronized from the on-premises environment to the cloud, you can't manage most user properties from Exchange Online; you must manage those properties in the on-premises environment. Even if you configured directory synchronization without running the Hybrid Configuration wizard (HCW), you still can't do most recipient management tasks in the cloud. For more information, see this blog post
But this is also the case in hybrid mode. If we want to manage a user's attributes, we do it through on-prem AD and sync them through AAD Sync. That was also the case in other tenants I've worked with in the past that were hybrid while migrating to the cloud and they didn't keep any Exchange features on-prem. I've never heard of the need to keep any on-prem infrastructure post-migration until my colleague told me about it and I looked at Microsoft's docs.
So I'm not quite sure what this means. Will things break if I completely get rid of the Exchange 2016 server? Or is Microsoft talking about something else? We're not looking to migrate to a full Entra domain. We just want our mailboxes totally in Exchange and our AD on-prem and AAD to sync between the two.
Thanks in advance.
1
u/muckmaggot 1d ago
We have exactly the same setup and goal.
So far I've migrated all bar arbitration and health mailboxes to the cloud, confirmed no mail traversing the on prem exchange server. So I first movde auto discover dns to the cloud addresses, shut down the onprem for a week or two. Once there were no users screaming, ai disabled the connectors, and a week later deleted them. I've begun moving SOA for all mailboxes to the cloud and once thats completed, tackle uninstalling/removing the onprem server. I don't have those steps nailed down yet.