Exchange 2013: Publish web services via Forefront TMG
Greg Taylor has published a nice guide to publishing Exchange 2013 web services on the Exchange Team Blog. All nicely illustrated with pictures. Unfortunately, Forefront TMG has been discontinued and support for Forefront UAG and Exchange 2013 is not yet available. http://blogs.technet.com/b/exchange/archive/2012/11/21/publishing-exchange-server-2013-using-tmg.aspx