We have just completed a staged migration from a single Exchange 2003 Server to Exchange Online (Office 365) using the guide, "Perform a Staged Migration of email to Office 365."

At the end of the guide, Microsoft warns: Decommissioning Exchange can have unintended consequences. Before decommissioning your on-premises Exchange organization, we recommend that you contact Microsoft Support.

The following have been accomplished so far:

• All on-prem mailboxes have migrated successfully.
• All on-prem users have been converted to mail-enabled users.
• Their mailboxes no longer exist in Exchange 2003, as part of the conversion to MEUs.
• DirSync is used to synch AD up to Office 365.

We plan to:

• Decommission Exchange Server 2003.
• Upgrade domain controllers from Windows Server 2003 SP2 to 2012 R2.

Since Exchange 2003 doesn't work in 2012 DFL/FFL, it most likely isn't possible to use any 2003 management tools to edit ADUC.

In this scenario, would you recommend to simply uninstall Exchange 2003?

Thanks!

• Edited by AMSYS Sunday, May 17, 2015 2:44 PM
• Moved by Jason Johnston [MSFT]Microsoft employee Monday, May 18, 2015 2:24 PM Not a development question.

Hi,

After you complete move all of your mailboxes to O365, DirSync will no longer be concern when you try to remove Exchange server.
Before you begin, please double confirm you have moved mailboxes to Office 365 successfully, the mail flow is ok and the user can access their mailboxes.
Additional, we can migrate the public folder to Office 365 if you need, please follow the link below:
https://technet.microsoft.com/en-us/library/dn874017(v=exchg.150).aspx

Meanwhile, heres an similar thread about Decommissioning Exchange 2003 after Office 365 Migration:
https://social.technet.microsoft.com/Forums/office/en-US/370ab979-a993-4859-8f6b-20eae06bc4d1/decommissioning-exchange-2003-after-office-365-migration?forum=exchangesvrgenerallegacy

Thanks