how Azure AD knows that mail belongs to Exchange On-Premise

Question

I had an Exchange server that is no longer operational, so accounts were created in AD, when we switched to azure, how can I know which users were created in an Exchange Server?

Answer 1

can you please provide more details about your current exchange and AD setup to help.

• is there any on-prem exchange currently in place. what is your messaging setup.
• are you running hybrid
• what you mean by switched to Azure. migrated all the mailboxes to office 365?

Answer 2

Hi @Juan Pablo CH

Please add some more information to the question.

As far as I understand, Did you mean:

1. You have a hybrid deployment (Exchange on-premises with Exchange online)
   However, the Exchange on-premises server no longer exists.
2. You would like to know which user mailboxes are hosted by the on-premises server

If I misunderstood your question, please feel free to correct me.

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If it is the case, I suppose you may achieve this by running some scripts in EXO powershell.
Here are two links which contain the detailed scripts for your reference:
Determine if a Mailbox is On-Premises or in Office 365 with PowerShell
Determine On-Premise and Cloud Mailbox Users
(Please Note: Since the web sites are not hosted by Microsoft, the links may change without notice. Microsoft does not guarantee the accuracy of this information.)

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