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Why Does the “Exchange Online-ApplicationAccount Already Exists” Error Happen? (With a Simple Fix)
I want to help you get past the “Exchange Online-ApplicationAccount already exists” error that pops up when you try to update Exchange 2019. This problem can stop your update and make you feel stuck. I’ll walk you through what causes it, show you how to fix it step by step, and help you get your Exchange update working again. My goal is to make this as simple as possible, using easy words and short sentences.
What Is the Error?
When you try to install a Cumulative Update (CU) for Exchange 2019, you might see an error that says something like:
The object ‘CN=Exchange Online-ApplicationAccount,CN=Users,DC=domain-name,DC=com’ already exists.
This message means Exchange tried to make a special account in Active Directory (AD), but it found that the account was already there.
Why Does This Happen?
- Exchange updates sometimes create or check for special accounts.
- If the account exists, but Exchange thinks it shouldn't, the update fails.
- This can happen even if you never used Hybrid mode or connected to Exchange Online.
- Sometimes, old updates or manual changes leave behind accounts that confuse the update.
What Did Not Work
First, I tried to fix it by removing the “Exchange Online” partner application with these commands:
Get-PartnerApplication Remove-PartnerApplication "Exchange Online"
But this did not solve the problem. The update still failed. The real problem was the leftover user object in AD.
How I Fixed the Error
Here’s how I fixed it, step by step:
- Opened Active Directory Users and Computers.
- Searched for “Exchange Online-ApplicationAccount” under the Users folder.
- Checked if the account was there.
- Make sure the account was not needed.
- Deleted the “Exchange Online-ApplicationAccount” object.
- After deleting the account, run the Exchange update again.
- This time, the update finished with no errors.
Why This Works
The update tries to create the account fresh. If the account is gone, Exchange can make it without problems. Removing only the partner application does not remove the AD user object; you must delete it directly in AD.
Extra Tips
- Always check if your server is in Hybrid mode before deleting accounts.
- Back up AD or make a snapshot before deleting objects, just in case.
- If you’re not sure, ask your IT team or a trusted advisor for help.
You can fix the “Exchange Online-ApplicationAccount already exists” error by deleting the user object from Active Directory. This clears the way for your Exchange update to finish. If you follow these steps, you should be able to get your update done without more trouble.