M365E5 - Mailboxes management

Melanie Tham 80 Reputation points
2025-12-01T02:32:01.31+00:00

Hi team,

I have a question around a scenario that we have within the organization. We have a number of employees that are changing role and currently being assigned with M365E5 licenses.

Due to the sensitivity information from current role, we prefer to have a brand-new mailboxes for employees on the new role while still maintaining the old mailbox for historical information purpose.

What is the best practice in licensing perspective other than having to allocate another E5 licenses to the employees during the migration?

Thank you .

Regards,

Exchange | Licensing
Exchange | Licensing

The framework for legally deploying and using Microsoft Exchange Server or Exchange Online, based on server and client access models.

Answer accepted by question author

AI answer

2025-12-01T02:32:10.95+00:00

In your scenario, where employees are changing roles and you want to maintain their old mailboxes for historical purposes while providing new mailboxes, the best practice from a licensing perspective would be to consider the following options:

  1. Use of Shared Mailboxes: Instead of allocating new licenses for the old mailboxes, you could convert the old mailboxes to shared mailboxes. Shared mailboxes do not require a separate license as long as they do not exceed 50 GB in size and do not have a user assigned to them. This way, you can retain access to historical information without incurring additional licensing costs.
  2. Archiving: If the historical data is not frequently accessed, you might consider using the archiving feature. This allows you to archive old mailboxes while keeping them accessible for compliance and historical reference, without needing to assign additional licenses.
  3. License Management: If new mailboxes are required and you want to avoid additional E5 licenses, you could explore the possibility of using lower-tier licenses for the new roles if the features required do not necessitate the full E5 capabilities. However, this would depend on the specific needs of the new roles.
  4. Cross-Tenant Migration: If you are migrating to a new tenant or organization, ensure that the licensing for cross-tenant migrations is properly managed, as this might also affect how you handle mailbox assignments.

It's essential to evaluate the specific requirements of the new roles and the compliance needs of your organization to determine the most suitable approach.

References:

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Answer recommended by moderator

Anonymous
2025-12-01T04:23:40.08+00:00

Hi @Melanie Tham

Thank you for posting your question in the Q&A Forum.

I understand that you are considering creating a new mailbox for employees moving to a new role, while keeping the old mailbox for historical purposes, and would like to avoid allocating additional E5 licenses if possible. 

Here is a detailed overview of possible approaches from a licensing and mailbox management perspective, which you may find helpful in deciding the best path forward: 

Convert Old Mailbox to Shared Mailbox 

  • A shared mailbox allows access to historical emails and calendar without consuming a separate E5 license, as long as the mailbox size remains under 50 GB. 
  • Users can access the mailbox in Outlook or add it as an additional mailbox. 
  • Shared mailboxes cannot be used to log in directly, but users with appropriate permissions can send emails as or on behalf of the mailbox.
  • For reference, more details can be found here: Convert a user mailbox to a shared mailbox - Microsoft 365 admin | Microsoft Learn 

This approach helps maintain historical data while minimizing licensing requirements. 

Provision a New Mailbox for the New Role 

  • Once the old mailbox has been converted or otherwise managed, the E5 license can be reassigned from the old account to the new mailbox. 
  • It’s recommended to review mailbox size, storage, and access permissions to ensure they meet your organization’s needs. 

Compliance & Retention Considerations 

  • If the old mailbox contains sensitive information or needs to be preserved for compliance purposes, you may consider converting it to an inactive mailbox. 
  • Inactive mailboxes preserve all content permanently while freeing up the license. 
  • To ensure data is retained securely, it is advisable to apply a Litigation Hold or Retention Policy to the mailbox before removing the associated user account or license. 
  • Further guidance is available here: Create and manage inactive mailboxes | Microsoft Learn 

You could consider converting the old mailbox to a shared mailbox if ongoing access to historical emails is needed, or to an inactive mailbox if the focus is on compliance and long-term archival. 

For the employee’s new role, a new mailbox can be created under the existing E5 license. It is highly recommended to apply Retention Policies or a Litigation Hold on the old mailbox to ensure sensitive data is securely preserved. 

This approach helps preserve historical information, optimize licensing, and aligns with Microsoft 365 best practices. 

I hope this provides some clarity on potential options, and I’m happy to provide further guidance if needed. 

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