Some administrators may not enable their users’ access to Outlook Web App over the Internet. For the users who have Outlook Web App blocked over the Internet, we recommend that WAC be disabled. You can do this by using the default setting or a custom OWAMailboxPolicy setting.
This TechNet article describes customizations and options that include the following key parameters:
When WAC is disabled, users will revert to downloading attachment contents to a local computer. The WebReady Document Viewing option isn’t available in Exchange 2013.
Article ID: 3135529 - Last Review: 24 Feb 2016 - Revision: 1