Mail and OCS Server Publishing using TMG on Forefront Unified Access Gateway (UAG) 2010
In a recent post I outlined some of the basic differences between Forefront Threat Management Gateway (TMG) 2010 and Unified Access Gateway (UAG) 2010. Although I indicated that UAG includes TMG under the covers, TMG is intended to provide protection for the UAG host only. It cannot be used to provide firewall, outbound proxy, or VPN services. There are specific instances when leveraging the underlying TMG services is allowed and supported. As the UAG Support Boundaries indicate, you can use TMG on UAG for Exchange mail server publishing (SMTP/SMPTS, POP3/POP3S, and IMAP/IMAPS) and Office Communications Server (OCS) SIP traffic publishing (Communicator Web Access (CWA) should be published using UAG). This means that if you are planning to publish Exchange and OCS, you can accomplish this using UAG alone. You are not required to deploy TMG or another firewall to provide secure access to mail server-to-server communication or OCS SIP traffic.
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Richard Hicks' Forefront TMG Blog 
This is good to know we get asked this frequently by customers. Can we also use to publish OCS web components?
Absolutely! My good friend and fellow Forefront Edge Security MVP Jason Jones has documented that on his blog – http://blog.msedge.org.uk/2010/10/publishing-ocs-2007-r2-web-components.html.