https://www.testexchangeconnectivity.com/ is a Microsoft owned site which allows the testing of the following:

Microsoft Exchange ActiveSync Test
Microsoft Exchange ActiveSync AutoDiscover Test
Microsoft Office Outlook 2007 AutoDiscover Connectivity Test
Microsoft Office Outlook 2003 RPC/HTTP Connectivity Test
Inbound SMTP Email Test

Note that not everything is working yet, I've had a few issues when testing the site, however it's definitely worth keeping an eye on. Thanks Microsoft!