Just a quick shout out to the excellent Exchange Remote Connectivity Analyser (ExRCA) which has proved invaluable to me in the last few weeks during an Exchange 2003 to Exchange 2010 migration. This migration required an extended period of coexistence between the two systems during which I wanted to ensure uninterrupted connectivity for all users both internally and externally. In addition we were deploying Microsoft Forefront Threat Management Gateway 2010 in the DMZ of the clients edge firewall to allow secure publishing of Exchange 2010 client access protocols.

This tool, from a web browser, simulates the connectivity of remote Exchange clients such as Outlook (over RPC), Exchange ActiveSync (iPad, iPhone, Windows Mobile, Android etc) and Outlook Web Access to your Exchange environment allowing you to quickly see and fix any issues that might prevent a user from connecting successfully to their Exchange mailbox.

What you get back is a detailed log, presented in the browser, of the connection attempt allowing you to quickly zoom in on any connection issues. Invaluable tool.