All About Microsoft published a list of features that aren't included in Outlook RT
Among them:Microsoft's Outlook RT preview: Which features are (and aren't) supported
No support for Online Archive or Personal Archive mailboxes
No ability to apply Messaging Records Management (MRM) retention policies
No Site Mailboxes
No support for Data Loss Prevention (DLP) policy tips
No Visual Basic for Applications (VBA) and COM Add-in support, no support for macros, add-ins or other custom programs (This is the same limitation that's imposed on all applications that are part of Office Home & Student 2013, which is installed as part of Windows RT and the RT 8.1 preview.)
No ability to set information rights management (IRM) on new email messages
No integration between Outlook 2013 RT and Lync (or any other of the Office Home & Student 2013 apps, for that matter
No integration with SharePoint, as the Outlook Contact Card does not display an active link to users' SharePoint My Site pages
No ability to add a fax account to Outlook 2013 RT
No ability to configure Outlook 2013 RT using Group Policy (same limitation as other Office Home & Student 2013 apps face)
