Some time since 26/07/19 and today (10/07/19) autodiscovery has stopped working for my domain.
On the 26th I was able to use autodiscover when setting up email addresses in Outlook 2016 but today it wants me to input the details manually. If I navigate to https://mail.mydomain.com/autodiscover/autodiscover.xml I get the message "autodiscovery must be provided a valid email address" so I wonder if this will help us resolve the issue.
I use cPanel email. When I try to get the manual set up details for the accounts in cPanel, it says the incoming and outgoing servers are mail.mydomain.com, but in the past it used to say n1plc.. etc.
Can you provide your actual domain so we can take a look at the DNS settings
The n1plc is more than likely the actual server name but if you have an SSL certificate install that "should work" as well - also the autodiscover error message is correct when you navigate to it via the browser as it's not passing the variables that Outlook passes
Here is a little test to see what error message maybe generated https://testconnectivity.microsoft.com/
Once your issue is resolved,
please be sure to come back and click accept for the solution