Exchange Online Mailbox Association with AD account on Premise

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Hello Experts,


is there any way to pull a report of Exchange Mailbox association with On-premise AD account


we have 2 AD forests and both are synching with Azure AD via AAD connect


We need to find how many mailboxes are still tied to Forest 1.

4 Replies

Could you please let us know what all information you need in the report. we can prepare a powershell script and shae with you. Incase if User Name, Display Name and Email address will help you, you can use below PowerShell scrip and run on Exchange online powershell to get the output-


Well you have the ImmutableID/SourceAnchor parameter, it's a 1:1 mapping between cloud and on-prem objects. Depending on your configuration, it can use different set of attributes, the default one being ObjectId for single-forest and objectSID/msExchMasterAccountSid for account/resource forest configuration. So check what you are using and then match the values between O365 mailboxes and the on-prem forest(s).

Hi @VasilMichev we use ObjectGuid/Immutble ID as 1:1 co-relation.


I went to AAD and did metaverse search based and added value as and i was able to pull the reports for users whos mailboxes are still mapped to


I hope i did correct.


@Vishal Kalal : Thanks buddy.


UPN/Displayanme/fORESTfqdn is what i am looking for? can i use your PS for same?

I don't see anywhere on Azure AD or Exchange Online where it specify Forest FDQN. Correct me If I am wrong.