Tuesday, February 9, 2016

Outlook 2016 - The connection to Microsoft Exchange is unavailable

This is a unique scenario, because it applies primarily to testing environments. I have a lab setup with Exchange Server 2016 and Outlook 2016. I was going a bit nuts because each time Outlook 2016 tried to configure the profile I got the following error message:
The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.
This error can occur when you get names wrong in your internal or external URLs. So, I verified the names in all of my internal and external URLs. I also tested connectivity in Outlook and the URLs from Autodiscover were correct. Also verified the names in the certificate.

It turned out to be an issue with the default gateway. As part the connection process, Outlook 2016 was attempting to connect with the default gateway (which didn't exist on my test network). When connectivity to the default gateway failed, Outlook provided that error.

To fix this, I pointed the client running Outlook 2016 at a valid IP for the default gateway. I used the IP of my domain controller. It's not important whether it's a router or not, it just looks for an IP that is alive. I've been too lazy to put a packet sniffer on it yet. I'm just happy it's working.

Short version: Make sure clients running Outlook 2016 have a valid default gateway.

Note: Credit to Stan Reimer who actually gave me the fix after it was discovered during development of a Skype for Business course

Update: For an explanation of why this happens, see this post: http://blogs.technet.com/b/rmilne/archive/2014/03/27/outlook-unable-to-connect-to-exchange-_1320_default-gateway-not-found.aspx


  1. Thank you so much for posting this. Had the exact same issue in my test environment, and couldn't figure out what was going on. You saved the day! :-)

  2. Thank you for this post. That help me so much. you saved my week.

  3. Thanks for the solution! This worked great once I changed the default gateway on my client machine to the DC IP address. Outlook was then able to connect without any issues.

  4. I got a similar situaition and this article saved me from the problem.
    Thank you so much!

  5. Same problem, same solution! Thank you, just amazing. All my Auto-Discovery were working perfectly, was just about at breaking point and about to install WireShark when I saw this.

  6. It works, but outlook takes much longer to connect exchange server in comparison that a real gateway with internet access is being used. I don't know the reason. about 20 seconds

    1. Newer versions of Outlook attempt to connect to Exchange Online as a first step. I suspect that needs to timeout first.