The Microsoft Exchange Remote Connectivity Analyzer, lets you run all sorts of tests against your exchange server implementation, released alongside of Microsoft Exchange 2010, it is one of the best utilities I have seen for Exchange so far.
Say if someone is having issues connecting to RPC over HTTPS, you can run the check, if it finds an error, it will tell you how to fix it!
Same goes with outgoing mail, you enter the external IP of the exchange server that smtp is sent out of, an email address from within the domain, and run a quick check, it will flag any errors and suggest fixes. It helped me fix an issue with a client just today.
This is the URL, https://www.testexchangeconnectivity.com
I wanted to leave it as such as its from Microsoft and you need to remember the URL