When enabling archiving for an Exchange mailbox user you may encounter the following error.
Mailbox ‘Alan.Reid' can't be archive-enabled because it has a managed folder mailbox policy assigned. Archives are supported only with a retention policy, the messaging records management (MRM) feature introduced in Exchange 2010.
To remove the managed folder mailbox policy from the mailbox user run the following PowerShell command.
Set-Mailbox alan.reid -ManagedFolderMailboxPolicy $null
You can then enable archiving for the mailbox user and assign a retention policy.