Is there a supported Exchange Hybrid procedure to convert the existing remote mailbox/user mailbox to a MailUser while retaining the existing mailbox content under Litigation Hold?

Hi @Kumar, Deepak, 

Thank you for the detailed questions. Based on the publicly available Exchange Online and Exchange Hybrid documentation, I have not found a Microsoft-supported procedure that converts an existing remote mailbox/user mailbox to a MailUser while simultaneously retaining the mailbox content under Litigation Hold on the same recipient object. The documented compliance-preservation model is the use of an Inactive Mailbox, rather than a MailUser that continues to own preserved mailbox data. 

From the information available: 

• A mailbox can be preserved for compliance purposes by placing it on Litigation Hold (or another qualifying hold) and transitioning it into an Inactive Mailbox state.  
• I have not located documentation confirming that the same recipient can then be represented as a MailUser while retaining the preserved mailbox under hold.  
• Therefore, the combination of"MailUser" and "preserved mailbox under Litigation Hold on the same recipient object" does not appear to be a documented or supported recipient lifecycle based on the available guidance. 

For your specific questions: 

1. The apparent conflict is between converting the recipient to a MailUser and preserving the Exchange Online mailbox as the mailbox associated with that same recipient object.  
2. I have not found documentation confirming that mailbox data can remain preserved under Litigation Hold after a supported conversion of that mailbox recipient to a MailUser. The documented preservation mechanism is an Inactive Mailbox.  
3. The supported alternative described in Microsoft guidance is to preserve the mailbox as an Inactive Mailbox for compliance purposes while maintaining the identity separately as required. 
4. If long-term retention is required, the documented path is typically through the Inactive Mailbox lifecycle. I have not found documentation confirming that the same underlying recipient can subsequently be converted to a MailUser without impacting the preserved mailbox.  

Because your question is specifically about the supported recipient lifecycle and configuration, rather than general retention behavior, I would recommend opening a Microsoft Support case if you require authoritative confirmation for a production design. The public documentation identified above does not explicitly describe or endorse a mailbox-to-MailUser conversion path while retaining the mailbox under Litigation Hold.  

The Global Admin should create a service request with Microsoft support to get advanced technical assistance and diagnostics. For detailed instructions on how to get support, please refer to Get support - Microsoft 365 admin.

I hope this helps clarify the currently documented behavior. If you receive any guidance from Microsoft Support, please feel free to share it here, as it would be valuable for others facing a similar Exchange Hybrid compliance scenario. 

Thank you again for your time and understanding. I really appreciate your patience, and I'm here to help. Looking forward to your response. 

If the answer is helpful, please click "Yes". If you have extra questions about this answer, please click "Comment".    

Note: Please follow the steps in the forum documentation to enable e-mail notifications if you want to receive the related email notification for this thread.