Decommissioning Exchange 2010 server in a hybrid O365 deployment.

Romo

I am working in the process and documentation of the decommission of an Exchange 2010 server in a hybrid Office 365 deployment and would like some opinions and experiences from you guys.

Specific Microsoft documentation about the subject:

According to the documentation, fully decommissioning the last Exchange server is not officially supported, especially not when DirSync is in use which it is in this case:

If the last Exchange server is removed, you cannot make changes to the mailbox object in Exchange Online because the source of authority is defined as on-premises. The source of authority refers to the location where Active Directory directory service objects, such as users and groups, are mastered (an original source that defines copies of an object) in a hybrid deployment. If you needed to edit most mailbox settings, you would have to be sure the Active Directory schema was extended on-premises and use unsupported tools such as Active Directory Service Interfaces Editor (ADSI Edit) for common administrative tasks. For example, adding a proxy address or putting a mailbox on litigation hold when there isn’t an Exchange Management Console (EMC) or Exchange Management Shell (Shell) on-premises becomes difficult and these simple (and other more complex) tasks cannot be done in a supported way.

Customers with a hybrid configuration often find after a period of time that all of their mailboxes have been moved to Exchange Online. At this point, they may decide to remove the Exchange servers from on-premises. However, they discover that they can no longer manage their cloud mailboxes.

When directory synchronization is enabled for a tenant and a user is synchronized from on-premises, most of the attributes cannot be managed from Exchange Online and must be managed from on-premises. This is not due to the hybrid configuration, but it occurs because of directory synchronization. In addition, even if you have directory synchronization in place without running the Hybrid Configuration Wizard, you still cannot manage most of the recipient tasks from the cloud.

Even though it is not officially supported they do provide a way to manually remove the hybrid deployment (link 1) and apparently the mailbox objects could be edited with ANSIEdit or other 3rd party tools.

Has anybody had any experience dealing with hybrid setups that would like to comment on their findings and experiences.

dbeato

@romo @Tim_G has written about this as below:
https://www.timothygruber.com/office-365/extend-ad-schema-exchange-2016-attributes-not-synchronizing/

Something to take in mind to remove the last Exchange.