Since Exchange 2010 SP1, when giving users Full access to another mailbox, they automatically get that mailbox added to their Outlook (2007 and up). This feature is called mailbox auto-mapping, and has made life a little easier for us IT administrators. But sometimes, you do not want a mailbox to be auto-mapped in Outlook for a particular user.
This can be achieved by setting the access permission through Powershell, and including the parameter -AutoMapping:$false in the cmdlet.
Add-MailboxPermission "Shared Mailbox" -User <user> -AccessRights FullAccess -AutoMapping:$false