Retention Defined
The word “Retention” has a different meaning in Office 365’s Exchange Online archive as compared to the Exchange Hosted Archive (EHA). In EHA the Retention Period value is a number representing the days to keep messages, for example 1,095 days would keep data for three years. In contrast, Office 365 Retention Policies have a different purpose and do not prevent users from deleting messages before the period has expired. Rather, in Office 365 you need to configure a feature called Litigation Hold with Duration (LHwD) to achieve EHA’s Retention Period functionality.

Legal/Litigation Hold Defined
EHA’s Legal Hold is closely aligned in functionality to Office 365’s Litigation Hold. In Office 365 you can configure Litigation Hold and this stops message destruction, just as turning on Legal Hold stops message destruction in EHA.

Office 365’s Litigation Hold with Duration Defined
Litigation Hold and LHwD are the same feature in Office 365. The ‘D’ is for duration. You can add a duration value to Office 365’s Litigation Hold (example 1,095 days = 3 years), which will keep messages until they are three years old based on the Received Date. LHwD is most similar to EHA’s Retention Period functionality. Note: Duration can only be set using PowerShell.

Users will have LHwD Automatically Set When Transitioned from EHA to Office 365
Transition will honor EHA retention and legal hold settings by setting LHwD on each transitioned Office 365 archive mailbox. For example, if your EHA company retention is set to three years, then all of your users will have LHwD=1095 (3 years) in Office 365. If your company is on Legal Hold than all of your users will have LH enabled in Office 365 (without duration which means keep all data forever, until LH is disabled).

You must set Litigation Hold on new users after transition from EHA
After your transition new Office 365 mailboxes that you create do not automatically have litigation hold enabled. There are two methods for enabling litigation hold on new users: The Microsoft Online Portal (MOP), which is the administrative web interface to Office 365; or by using PowerShell. Only PowerShell is able to set a Litigation Hold with Duration, meaning you can turn on Litigation Hold in MOP, but you cannot set a duration.

To enable LH using MOP

  • Login to MOP as an administrator.
  • On the Admin page click the Manage link under the Microsoft Office 365, Exchange section.
  • In the Search Mailboxes field search for the mailbox for which you want to enable litigation hold.
  • Double click the mailbox to open its properties and then expand the Mailbox Features section.
  • You can set Litigation Hold by highlighting the setting and clicking the Enable button.

The following examples are PowerShell syntax that can be used to enable Litigation Hold with Duration:

This PowerShell script will set all users to LH Enabled with no duration.
     Get-Mailbox -ResultSize unlimited | set-mailbox -LitigationHoldEnabled $true

This PowerShell script will enable LH on all users for a duration of 1,095 days (3 years).
     Get-Mailbox -ResultSize unlimited | set-mailbox -LitigationHoldEnabled $true
     Get-Mailbox -ResultSize unlimited | set-mailbox –LitigationHoldDuration 1095

This PowerShell script will enable LHwD on a single user with the primary e-mail of
     Set-Mailbox -LitigationHoldEnabled $true
     Set-Mailbox -LitigationHoldDuration 1095

For information about how to use PowerShell, visit the Use Windows PowerShell to manage Office 365 page.

How message destruction works in Office 365
Message Destruction in Office 365 is performed by the MRM (Messaging Records Management) service. This service runs in the background automatically. Message destruction is calculated based on the Received Date of the message. For example if you have litigation hold without a duration set, then the MRM does not delete messages. If you have LHwD set to 1,095 days (3 years), then each time the MRM runs it is determining if the message’s age is greater than the Received Date plus 1,095 days. If yes the message is deleted.

How LH Preserves Messages
Users can still delete messages from their Inbox when LH is enabled. When this happens the message is stored in the Recoverable Items folder. For detailed information on how messages are retained, please visit the Put a Mailbox on Litigation Hold page.

See Also