*please note, I've changed the question in response to the suspicion that this site is dubious.
I found this today - https://www.testexchangeconnectivity.com/
Pretty nifty! (or maybe not?)
There's a post about this site on a site called msexchangeteam.com.
They claim to be the "official blog of the Microsoft Exchange Team".
There's also a facebook group for this tool here.
I used the testexchangeconnectivity tool today - perhaps this was foolish.