1 First: Always check Certificates and DNS
1.1 Check if your certificates are configured correctly and if they have expired.
Open the Exchange Management Console and run: Get-ExchangeCertificate | fl
Review your certificates and ensure that they have not expired
A good way to test DNS is using NSLOOKUP. Open cmd and type nslookup and hit enter.
(In our case we need to run nslookup to our client’s autodiscover address to test redirection as we user autodiscover redirect.)
Type autodiscover.yourdomain.com (or .net etc.) this should return with the redirect address as per below screenshot.
1.3 Additional Tests
You should also run the below tests in Outlook and in a Web Browser to test Autodiscover:
Hold Ctrl and Right click on the Outlook Icon in the task bar. Then choose “Test E-mail AutoConfiguration”.
Within the dialog box type your e-mail Address, password and untick Use Guessmart and Secure Guessmart Authentication. Then click on “Test”
The test should be successful with doing a redirect.
You could also test autodiscover using http://testexchangeconnectivity .com but make sure there is no mail in the mailbox and OoO is not on as it will spit out an error.
2 IIS Settings
We found that the problem we had had nothing to do with DNS or Certs but the tests still failed. While testing the rules on ISA we saw an entry that pointed us to the following location.
Right Click on AutoDiscover.xml ans untick the following tick box.
This resolved the issue and all AutoDiscover tests where successful. OoO and OAB was working once again.
Note: When we restarted IIS we noticed that the tick was back and we had to untick the checkbox again. We are still looking into this.