A retention tag is a mechanism to apply retention settings to mailbox folders and individual items. Retention tag settings specify how long a message remains in a mailbox, and the action to be taken when the message reaches the specified retention age.

In Exchange 2010, you can create three types of retention tags.

1. Retention Policy Tag (RPT)   Retention Policy Tags apply retention settings to default folders such as Inbox, Deleted Items, and Sent Items. Mailbox items in a default folder with a RPT applied inherit the folder's tag. Users cannot apply a different tag to a default folder, but they can apply a different tag to items in a default folder.
   You can create RPTs for the following default folders:
   
   • DeletedItems
     
   • Drafts
     
   • Inbox
     
   • JunkMail
     
   • Outbox
     
   • SentItems
     
   • RssSubscriptions
     
   • SyncIssues
     
   • ConversationHistory
     

   Important:
   You can't include more than one Retention Policy Tag for the same default folder type in one retention policy. For example, if a retention policy has a tag of type Inbox, you can't add another RPT of type Inbox to that retention policy. In Exchange 2010, Retention Policy Tags are not supported for the Calendar, Contacts, Journal, Notes and Tasks default folders.

2. Default Policy Tag (DPT)   Default Policy Tags are created to apply retention settings to untagged mailbox items. Untagged items are mailbox items that do not have a retention tag applied to them either by inheritance from the folder they are located in, or applied explicitly by the user. DPTs are created by specifying the type All. A retention policy should not contain more than one DPT.
   
3. Personal Tags   Personal Tags are retention tags available to users as part of their retention policy. Users can apply personal tags to folders they create or to individual items. For example, you can create a Personal Tag to allow users to tag messages that are business critical, a higher message retention age of 3 years, and the MoveToArchive retention action to move the messages to the user's archive mailbox after 3 years.
   

When specifying the retention action taken on a mailbox item reaching its retention age, you can select from one of the following actions:

• Move to archive   The Move to archive action moves a message to the user's archive mailbox. Messages are moved to a folder in the archive mailbox with the same name as the source folder in the user's primary mailbox. This allows users to easily find messages in their archive mailbox. For more details about archive mailboxes, see Understanding Personal Archive.
  
• Move to the Deleted Items folder   The Move to the Deleted Items folder action moves messages to the Deleted Items folder. This emulates the behavior experienced by users when they delete a message. Items in the Deleted Items folder can be moved back to the Inbox, or any other mailbox folder. Depending on the user's mailbox settings in Outlook Web App or Outlook, the Deleted Items folder may be emptied when the user logs off Outlook Web App or closes Outlook. You can also create a Retention Policy Tag for the Deleted Items folder to take the required action on messages in the folder after a certain period.
  
• Delete and allow recovery   The Delete and allow recovery action emulates the behavior when the Deleted Items folder is emptied or the user hard deletes a message. When this happens, and deleted item retention is configured for the mailbox database or the user, messages move to the Recoverable Items folder. Recoverable Items, also known as "dumpster", allows the user another chance to recover deleted messages. For more details about recoverable items, see Understanding Recoverable Items.
  
• Permanently delete   The Permanently delete action permanently deletes a message. When this action is applied to a message, it is purged from the mailbox. This action is akin to a deleted message being removed from recoverable items. Once this happens, the user can no longer recover the message.
  

  Important:
  If Legal Hold is enabled for a mailbox user, although the messages are permanently deleted and no longer recoverable by the user, Multi-Mailbox Search will return the message in search results. For more details, see Understanding Multi-Mailbox Search.

• Mark as past retention limit   The Mark as past retention limit action marks a message as past retention limit. Supported Outlook clients - exOutlook2k7 and later, display messages that are past their retention limit using strikethrough text. Users who use a supported client notice the changed display and recognize the message as expired, following which they can be encouraged to take further action such as deleting the message, or moving it to the archive mailbox. This action is intended to allow you to make expired messages noticeable, and encourage them to follow the organization's messaging policies, without taking a drastic action such as deleting the message. It can be used as the initial step to create awareness about MRM.
  

For more information about how to create retention tags, see Create a Retention Tag

Retention policies allow you to group one or more retention tags and apply them to mailboxes. A mailbox cannot have more than one retention policy. Retention tags can be linked or unlinked from a retention policy at any time.

A retention policy can have the following retention tags:

• One or more RPTs for supported default folders.
  

  Note:
  You can't link more than one RPT for a particular default folder such as Deleted Items to the same retention policy.

• One DPT of type All,
  
• Any number of personal tags.
  

Although you can add any number of personal tags to a retention policy, a large number of personal tags with different retention settings can confuse users and affect the user experience. We recommend linking no more than ten personal tags to a retention policy.

Note:
Although a retention policy can exist in a state where it does not have any retention tags linked to it, it is not a recommended scenario. A mailbox with a retention policy which does not have any retention tags linked to it may result in mailbox items not expiring.

For more information about creating a retention policy, see Create a Retention Policy.

For more information about applying Retention Policy to mailboxes, see Apply a Retention Policy to Mailboxes.

The Managed Folder Assistant is a process that runs on mailbox servers and processes mailboxes that have a retention policy applied. It applies the retention policy by inspecting items in the mailbox and whether they are subject to retention. The assistant stamps items subject to retention with the appropriate retention tags, and takes the specified retention action on items that are past their retention age. The assistant runs on a specified schedule. By default, it is scheduled to run daily between 1:00 a.m. to 4:00 a.m. You can schedule the assistant to run at a time when the mailbox server is relatively idle or not under a heavy load. When determining a schedule for the assistant, you must consider other processes that compete for mailbox server resources, such as offline defragmentation of the mailbox database and antivirus scans.

Note:
The assistant does not take any action on messages that are not subject to retention, specified by setting the retention tag's RetentionEnabled property to false. You can also set this property to false to temporarily suspend items with a particular tag from being processed.

For more information about scheduling the Managed Folder Assistant, see Schedule the Managed Folder Assistant.

Default folders such as Inbox, Deleted Items, and Sent Items get RPTs applied as specified in the retention policy. Users cannot change RPTs associated with default folders. However, a personal tag can be applied by a user to an item in a default folder, thereby causing the item to have a different retention setting than the folder it resides in. Similarly, a user can also assign one personal tag to a user-created folder, but a different personal tag to an item in that folder.

A mailbox item moved from one folder to another inherits any tags applied to the folder it is moved to. If an item is moved to a folder that does not have a tag assigned, the default policy tag is applied to it. If the item has a tag explicitly assigned to it, the tag always takes precedence over any folder-level tags or the default tag.

When a retention tag is removed from the retention policy applied to a mailbox, the tag is no longer available to the user and cannot be applied to items in the mailbox.

Existing items which have been stamped with that tag continue to be processed by the assistant based on those settings, and any retention action specified in the tag is applied to those messages.

However, if you delete the tag using the Remove-RetentionPolicyTag cmdlet, it removes the tag definition stored in Active Directory. The next time the assistant runs, it processes all items that have the removed tag applied, and restamps them. Depending on the number of mailboxes and messages, this processing may result in significant resource consumption on all mailbox servers which have mailboxes with a retention policy that included the removed tag.

Important:
If a retention tag is removed from a retention policy applicable to mailbox, any existing mailbox items with the tag applied will continue to expire based on the tag's settings. To prevent the tag's settings from being applied to any items, the tag should be deleted. Deleting a tag removes it from any retention policies it is included in.

You can disable retention for a retention tag. This results in the assistant ignoring items which have that tag applied. Items that have a retention tag applied with retention disabled never expire. They are not considered as untagged items, and therefore the Default Policy Tag does not apply to them. For example, you can disable a retention tag temporarily to stop the assistant from processing messages with that tag when troubleshooting retention tag settings. You can also consider disabling a retention tag before you decide to remove it.