Outlook fails to connect to older exchange server

This can happen due to differences in TLS/SSL version compatibility or ciphers.

To fix it from the client end (e.g. the desktop system that runs Outlook)

You need to create the registry key "ExcludeHttpsRootDomain" as a DWORD give it a value of 1. See below for the location.

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover\]
"ExcludeHttpsRootDomain"=dword:00000001

Then make sure you close all of Outlook products.

Then go to Control Panel -> Mail (Microsoft Outlook) (32-bit)
Add an account
Put in the details (do not use the manual setup)
If it prompts for a user/pass make sure you edit it and put the email address as the user and the correct pass

It should now succeed with autodiscover and add the mail account without issue.