If you've created your custom domain name - Microsoft doesn't walk you through the whole process of pointing your domain to O365. I just went through this same craziness. From the threads I followed, I was headed down a rabbit hole of running MOSDAL to obtain logs in order to find out why autodiscovery wasn't working with desktop Outlook on my domain name. It turns out that the answer was very simple. You have to move your name servers to MS Online services. To do that:
- go to your O365 Admin page.
- Click on Domains in the left pane.
- Click on the radio button next to your custom domain name.
- Click on the Troubleshoot hyperlink above (and below) the domain names list.
- This will then walk you through the process to properly move your name service to MS's based on your DNS service provider.
That does it. For some reason, the O365 setup only walks you through confirmation of your domain name; and then falsely reports to you that the process is complete. If you're moving the entire domain (make sure you don't have a web site on that domain setup elsewhere); then following the instructions above will fix everything.