Microsoft Application Request Routing (ARR) is a proxy-based routing module for IIS that forwards HTTP requests to content servers based on HTTP headers, server variables, and load balance algorithms. After my recent posts on reverse proxy servers and Exchange Server I received a few emails about using ARR as a reverse proxy for Exchange Server. The Exchange Team recently released some guidance on how to achieve this on their blog for those of you who are interested in this setup, here is a link to the post.