Moved al mailboxen to Office 365 & Still using dirsync! Can you remove the last Exchange 2010/2013 Server. Yes It Can! Just don’t do it!! You will have a support issue when you have problems!!

After a customer migrated  to Exchange Online some time ago.
They wanted not a hybrid situation. but they are using still DirSync!

After reading: Decommissioning your Exchange 2010 servers in a Hybrid Deployment a I read its not a real problem.

Changed DirSync & After that Uninstalling Exchange 2013 was very easy.

I had only to disable the Arbitration mailboxes: I did that with the following powershell command:

Get-Mailbox -Arbitration | disable-Mailbox -arbitration -RemoveLastArbitrationMailboxAllowed

I did not publish this article because i has still some doubts!!

I had still a question: Do want to remove the last Exchange Server? Have you a supported Environment without a local Exchange Server and still using DirSync??

Yes & No!!

After reading Concerning Trends Discovered During Several Critical Escalations

Microsoft Says:
You may remove the last Exchange Server locale when you move totally to Office 365/Exchange Online, but change Exchange Attribuuts trough ADSI is not supported.

If you don’t have a third party tool for that. The only way is trough ADSI and that is not supported.

My Conclusion:

You have a support issue when you dropped a Call at Microsoft and they investigate your environment.
Don’t remove the last Exchange Server even when all mailboxen exist in Office 365/Exchange Online and keep them up to date!
You can always install a Exchange Server but most of the times it will be always to late!