·To remove retention policy from Outlook:
When you remove a retention policy from an email message, the folder policy applies to the item, if one is assigned.
1. In the message list, click a message. (To select more than one message, press and hold CTRL as you click each message.)
2. On the Home tab, in the Tags group, click Assign Policy.
3. Under Retention Policy, click Use Folder Policy.
Note: The retention policy for a message appears in the header in the Reading Pane under the recipient names and includes the expiration date. If no retention policy is applied, no information appears under the message recipient names.
You can use the following exchange cmdlet: http://technet.microsoft.com/en-us/library/dd297962.aspx. Please note that the retention policies are used to apply message retention settings to folders and items in a mailbox.
The below cmdlet removes an existing retention policy "Business Critical", which is assigned to users, and suppresses the confirmation prompt.
> Remove-RetentionPolicy -Identity "Business Critical" -Confirm:$false -Force