I'm sure this is new in CRM 2013 as I have never come across this message before. But basically one of my users was creating an appointment and clicked on save, they then got a message at the top of the screen stating 'Some recipients are outside your
organization, These recipients will also receive this appointment when you save it'. It allows me to save as this was not an error message however I have never seen this message before. I'm struggling to replicate this message where I have added
various Contacts into the required field. I have a screenshot of the message so the user did definately get this message.