Hi Kelsey,
Edge Transport servers deployed with Microsoft Exchange are deployed in an organization’s on-premises perimeter network. They’re non-domain-joined computers that handle Internet-facing mail flow and act as an SMTP relay and smart host for Exchange servers in your internal network.
If you need detailed information about this problem, please click on the two following links.
http://technet.microsoft.com/en-us/library/hh945224(v=exchg.141).aspx
http://technet.microsoft.com/en-us/library/dn151300(v=exchg.150).aspx
Thanks,
Yang Yu