Preserve mailbox data for eDiscovery using inactive mailboxes in Exchange Online

In Exchange Online and Exchange Server 2013, you can use In-Place Hold or Litigation Hold to preserve mailbox content for litigation or investigations. Many organizations also need to preserve mailbox data for users who are no longer in the organization.

In on-premises Exchange deployments, this has typically been done by disabling the Active Directory user account and performing actions such as removing it from distribution groups, preventing inbound/outbound email to and from the mailbox (including setting delivery restrictions and configuring message size limits), hiding the mailbox from the Global Address List (GAL), and also setting an account expiration date on the user account in Active Direcory. Licensing costs are not a concern in this scenario, because you do not need a Client Access License (CAL) for a mailbox that’s no longer active.

In Exchange Online, admins remove mailboxes for departed users. However, once you remove a mailbox, it can no longer be included in In-Place eDiscovey searches (Multi-Mailbox Search in the previous version of the service and in Exchange 2010). Additionally, 30 days after you remove a mailbox, it is permanently deleted from Exchange Online and can no longer be recovered. In-Place eDiscovery requires that the mailbox be active, which means an Exchange Online or Office 365 plan is required for the mailbox for as long as you want to preserve data for eDiscovery.

Note: You can preserve mailbox data offline by exporting it to a PST file using Microsoft Outlook and then remove the mailbox. However, if you need to perform an eDiscovery search, you would need to inject it back to an Exchange Online mailbox.

Inactive Mailboxes

In the new Exchange Online, we’ve introduced the concept of inactive mailboxes to handle departed users. When a user leaves the organization and you need to retain their mailbox data for some time to facilitate eDiscovery (or meet retention or business requirements), you can place the mailbox on In-Place Hold or Litigation Hold before removing the Office 365 user. This preserves the mailbox, but prevents it from sending/receiving messages, hides it from users so it's no longer visible in the GAL and other recipient lists. You can add inactive mailboxes to In-Place eDiscovery searches. Inactive mailboxes do not require an Exchange Online or Office 365 plan.

When your eDiscovery, retention or other business requirements are met and you no longer need to preserve the mailbox content, you can remove the mailbox from In-Place Holds or Litigation Hold. After you remove hold, the normal mailbox removal behavior of Exchange Online will resume for the mailbox – which means, if the mailbox was removed more than 30 days ago, it will be permanently deleted. If it was removed less than 30 days ago, it will be permanently deleted after 30 days of removal.

For more details, see Managing Inactive Mailboxes (short url: in Exchange Online documentation.

Inactive mailboxes are available in March 2013 in the E3, E4, A3, A4, G and Exchange Online P2 plans.

Migrating inactive mailbox data to Exchange Online

If you already have inactive mailboxes in your on-premises Exchange 2010 or Exchange 2013 environment or a third-party archive, you can move the data to inactive mailboxes in Exchange Online by first provisioning an Exchange Online mailbox, which requires a plan subscription, importing the data to the Exchange Online mailbox, placing the user on In-Place Hold or Litigation Hold and then deleting the user account, making it an inactive mailbox. You do not require a plan subscription for that mailbox after you make it inactive. However, you will need a subscription during the provisioning and data import process. If you have a large number of inactive mailboxes, you can provision them in batches using a smaller number of subscriptions. Note, the Product Usage Rights (PUR) states that licenses can only be reassigned once every 90 days.

How long can a mailbox be inactive?

You can preserve data in inactive mailboxes for as long as you need to, based on your organization's retention and eDiscovery requirements. Of course, you would need to continue to be an Office 365/Exchange Online customer.

How can you remove data from an inactive mailbox?

If you've specified a hold duration using In-Place Hold or Litigation Hold, items older than the hold duration are removed when the Managed Folder Assistant (MFA) processes the mailbox.

Bharat Suneja


  • 3/16/2015: Changed the highlighted verbiage (in Migrating section) from "placing the user on In-Place Hold or Litigation Hold and then removing the subscription, making it an inactive mailbox" to "deleting the user account". Added links to In-Place eDiscovey and Litigation Hold.
  • 5/23/2013: Added info about migrating inactive mailbox data to Exchange Online.
  • 6/18/2013: Added note about Product Usage Rights (PUR).
  • 3/5/2014: Added info about how long a mailbox can be inactive and included Litigation Hold.
  • 4/14/2014: Added clarification about how you can remove data from inactive mailboxes (and hold duration specified for In-Place Hold or Litigation Hold has no impact.)
  • 1/27/2016: Updated above clarificaiton about how you can remove data from inactive mailbox to state it is processed by MFA and items older than LitigationHoldDuration are removed. Removed: All content in an inactive mailbox is on hold until you remove the hold from the mailbox.
Comments (12)
  1. Tom Mucha says:

    Great feature!  Are there any limitations to the length of the hold or mailbox size?

  2. OceanOB says:

    Any plans to include such a good feature in the long awaited Exchange 2013 CU1 on-pemises? Or in a later one?

  3. says:

    What about for users who only have an Exchange Online Plan 1?  I believe the service description says In-Place hold is only available for Exchange online Plan 2 users.  

  4. tom says:

    I like that Exchange Team has also included Exchange On-Premises info here too.

    Please remember you have many Exchange On-Premises customers world-wide and we want to Stay On-Premises.


  5. Bharat Suneja [MSFT] says:

    @Tom Mucha: No limitation on the length of hold – as long as you are an Exchange Online customer. Max mailbox sizes depend on the plan – most plans cap at 25 GB for primary & archive. Some plans include an unlimited archive. See

    Exchange Online Service Description
    > Mailbox Types and Storage Limits for details.

  6. Bharat Suneja [MSFT] says:

    @dafsdfasdfsadfsdfsd: As stated in the post, inactive mailboxes are not offered in Exchange Online Plan 1. You would need to change to Plan 2.

  7. Bharat Suneja [MSFT] says:

    @Tom: Certainly, and therefore the comparison with on-premises.

    Many customers prefer to stay on-premises, and features like inactive mailboxes is where on-premises has been at an advantage, whereas Exchange Online customers have had to pay to maintain a mailbox for departed users in the past if they wanted to retain the content and include it in eDiscovery.

  8. Mike Campbell says:

    This is great news.  I know it opens the door for Exchange Online adoption for some customers that I have been working with.  

  9. John says:

    Not enough Exchange 2013 On-Premises Articles here.

    Exchange Team your customers worldwide want more Exchange 2013 On-Premises Articles.

  10. Patel says:

    I agree with John. We (your worldwide Exchange On-Premises customers) want to see more Exchange 2013 On-Premises articles here.

  11. lee says:

    Agree with John & Patel. We need more Exchange 2013 On-Premises articles here.

    Come on Exhcange team do not forget about your customers.

  12. Bharat Suneja [MSFT] says:

    @Lee, Patel & John: This blog is still (heavily) focused on Exchange Server and on-premises deployments. A quick glance at the last 10 post shows 8 of them apply to on-premises. This post also covers how you typically handle inactive mailboxes in on-premises deployments.

Comments are closed.