Exchange 2013 -- How do I determine if an internal email was sent internally versus sent over the internet

Hi all

I want to determine if I have setup my environment correctly

To that end when an internal user sends an email to another internal user is it possible to see the mail flow path

i.e. did the mail remain within the environment versus was the mail sent out over the internet and back again

The users are connected via outloook

Thanks

Tadhg

Tadhg Concannon