Outlook 2016 will not connect to Exchange 2016 following SSL install

We have a new build Exchange 2016 server (on Server 2012 R2) and several Outlook 2016 clients. When we attempted to connect the clients with the default settings on Exchange (no SSL added, namespaces not changed etc.), apart from a certificate error which we could ok to continue, the clients connected properly.

Today, we added a GoDaddy SSL and changed all our namespaces to the external address e.g. office.domain.com. Now, the clients still give the certificate error but they also won't connect to Exchange with the error :

The action cannot be completed the connection to Microsoft exchange is unavailable outlook must be online or connected to complete this action.

We have an identical setup in two other offices (none are linked) and they work perfectly with the same settings. We have double checked their namespaces, DNS, IIS bindings and run Outlook test settings, but nothing will make these clients connect. The only difference is the faulty office is using Cumulative Update 2.

I'm slowly going insane here so would greatly appreciate any help to resolve this. I have tried rolling one client back to Office 2013 but get the same error.
Hector JonesAsked:
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Hector JonesConnect With a Mentor Author Commented:
An update to this, I raised a support call with Microsoft and the problem was that IIS authentication was completely blank, something he had never seen before. He restored that and everything works perfectly now.
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Jeffrey Kane - TechSoEasyPrincipal ConsultantCommented:
Outlook 2016 uses only Autodiscover to connect to an Exchange Server.  If you've created a Forward Lookup Zone for your external domain in your Windows DNS, you need to be sure you also have the proper autodiscover record included (generally just a cname record which points autodiscover to server.domain.com).

To troubleshoot, from a workstation you can hold CTRL down and right click the Outlook icon in the status area of the taskbar to select "Test e-mail autoconfiguration" and it will step through what Outlook is seeing as it tries to connect.
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Jeffrey Kane - TechSoEasyPrincipal ConsultantCommented:
Oh, and if you've done all that then just create a new Outlook profile for the affected systems.
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Hector JonesAuthor Commented:
Thanks Jeffrey, I've run the Outlook Test email configuration and it all looks correct and (apart from unique office name of course), completely matches the other two offices configuration.

I've also tried creating new profiles but get exactly the same error on all the machines.

I've just re-checked all namespaces, both via the gui and PowerShell and everything is exactly as it should and have triple checked DNS can resolve both internally and externally.

I actually wish I could find an error somewhere to fix, but these clients just will not connect.
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Jeffrey Kane - TechSoEasyPrincipal ConsultantCommented:
Then your next step is to download and run the Microsoft Connectivity Analyzer Tool found here:  https://testconnectivity.microsoft.com (on the "Client" tab)
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Todd NelsonSystems EngineerCommented:
Try restarting the Autodiscover App Pool on the Exchange server where the mailbox resides; or restart the server if you haven't already.

https://oddytee.wordpress.com/2016/08/16/outlook-client-does-not-connect-to-mailbox-on-exchange-2016/
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Hector JonesAuthor Commented:
Thanks again for the help.

The server has been restarted and I've restarted the Autodiscover pool, no change. These are all new mailboxes on a new server although we did pst mailboxes over via Outlook from our old SBS2008 server.

I ran the Analyzer from the Client tab and it fails on AutoDiscovery connectivity. Everything else it passes. Looking at the failure though, it is looking just at domain.com but our namespace uses office.domain.com. Is the Analyzer confused or have I missed something ?

I've also just run the Analyzer on a client pc in another office that works perfectly and get the same failure, again it seems to look at domain.com not office.domain.com.
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Hector JonesAuthor Commented:
Resolved by Microsoft support.
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