Microsoft Exchange Team has released the Exchange Server Remote Connectivity Analyzer.
This tool helps you ensure that your Exchange internet services like Autodiscover, ActiveSync, Outlook Anywhere, Inbound SMTP have been configured correctly.
Exchange implementers! Bookmark this website: www.TestExchangeConnectivity.com
In the current release, the tool can check Exchange ActiveSync on Windows Mobile 5 and third party devices. It can also check Outlook Anywhere on Outlook 2003 and Outlook 2007 with Autodiscover.
For more information on the tool and a video, check out the Exchange Team blog.