Outlook protection rules automatically apply Information Rights Management (IRM) protection to messages in Microsoft Outlook 2010, based on message conditions that include the sender’s department, who the message is sent to, and whether recipients are inside or outside of your organization. When an Outlook protection rule is enabled, Outlook 2010 inspects messages before they are sent and applies a rights management services (RMS) template if a message meets the conditions of the rule.
Now Outlook Web App also support Protection Rule in Exchange 2013 , yes they were not supported in Exchange 2010. Read below two sources from Microsoft and compare the statements.
In Microsoft Exchange Server 2013, Microsoft Outlook, and Microsoft Office Outlook Web App, users can apply Information Rights Management (IRM) protection to messages by applying an Active Directory Rights Management Services (AD RMS) rights policy template.
In Exchange 2013, Outlook protection rules help your organization protect against the risk of information leakage by automatically applying IRM-protection to messages in Exchange 2013. Messages are IRM-protected before they leave the Outlook client. This protection is also applied to any attachments using supported file formats.